I had a feeling that the Nats farm system was ok but top heavy, meaning Turner's graduation and the cooling on Giolito would have significant effects. I went back and looked and saw the Nats system ranked pre-season anywhere from 5th to 17th. I lean more toward the latter. So let's look at some top and mid-level prospects and see what kind of interest teams might really have.
The Big 4
Giolito - Was basically the most prized pitching prospect going into last year but he didn't live up to that highest of high hype last year. He was in and out of the majors and each time in was a failure. He was hittable and gave up a ton of homers, 7 in 21 innings. There was also questions about a decrease in velocity which is a big deal for someone who already had arm surgery. And his AA numbers arguably took a step back. Still, he will be only an "old" 22* next year and everyone loves his stuff. His AAA numbers last year are exactly what you want to see. He's a 2017 or 18 full time player. The idea of him coming into the majors and immediately being a #1 type may be fading, but the idea of him being a very successful pitcher a few years down the line has not. His stock will drop a bit probably from Top 3ish to Top 10ish, but with very watchful eyes those first couple months.
Turner - off the table
Robles - A name that got a lot of attention as he did really well in A ball as a "young" 19 year old. He didn't do as well in A+ ball but he did better in his second stint after injury. There's a question on whether he gets power but right now the promise of his age wins out. Likely moves from a Top 30ish prospect to a Top 15ish. If he develops power he'd be a Top 10. Optimistically projects for a 2019 full-time role at 21-22.
Lopez - Like Giolito his time in the majors wasn't great, but unlike Lucas there were times you could point to what he was doing and feel good. Sure, about half of them were against the Braves but you gotta start somewhere. There was a lot of talk about him "breaking through" and maybe being better than Giolito as his K's went way up in AA this year. But they went back down in AAA, and dialing things up in MLB to get more meant a big increase in wildness. Like Giolito he's a 2017-18 full time player. Like Giolito I think that ranking is very tentative and could change radically in either direction based on just the first couple months. Unlike Giolito I'd expect his pre-sesaon stock to rise from a back quarter of Top 100 to a Top 50 ish player.
The next tier
Glover - Live arm who showed potential dominating AA with Ks and AAA with control. Trajectory says its hard to see how he doesn't end up set in a major league pen next year, if not to start then sometime. Could be a potential lights out closer - however that's a phrase tossed around for a lot of live minor league arms. Will break Top 100, probably in Top 75.
Cole - I'd love for Cole to get into the Top 100 of someone's list again because I bet he'd be the only guy to ever be ranked in someone's Top 100 in 6 different seasons. 2016 though was the first time he wasn't and nothing about last year changes that. Might develop into a back end starter but at 25 and looking at his 4th year in AAA he's more of a throw-in than a key piece.
Difo - The anti Giolito/Lopez, Difo was not bad in the majors, but in the minors he did nothing to raise his stock. His brief flirtation with pop in 2014 has faded and he's back to being seen as a speedy slap hitter. It's not entirely clear where he fits now. Major league bench? AA? I'd imagine most see him as a AAA which means 2016 is a make or break year for the "young" 25 year old if he's going to be a starter in the majors.
Fedde - He's on the cusp of being a top prospect and should be in the bottom of a few Top 100s. There is simply no doubt he is pitched better in 2016 than 2015. His A+ stats suggest the special pitcher teams thought he could be, but his subsequent finish in AA gives you a bit of pause. Where his ceiling now is a question. Does he keep getting better and become a real rotation prospect? He's roughly on target age (24 in 2017) but that means if the AA year goes poorly he'll start to be on the older side.
Voth - Everyone loves Voth and he'll break into some Top 100s. However the fancy stats don't really like him as he's not particularly good at striking out batters or having super control. I can't look at that and think the Nats didn't move him up to protect him from being exposed by major league hitting. But whatever, you have what you have and what you have is a guy that has shown he is not easy to get hits against in the minors. On the other hand, he did make the AFL and hasn't been all that impressive.
The other AFL hitters
Osvaldo Abreu - did nothing in AFL. did nothing in A+ ball. Not old but kind of stalling out. Difficult to see as a real prospect anymore, but has next year to change that.
Drew Ward - hitting for average in AFL. Nats have been aggressive in their moving of him and he's generally done just enough to justify confidence but last year's AA wall was slammed into. Not a top prospect but he's only 22 next year so next year won't be make or break.
Andrew Stevenson - hitting for average and power in AFL. Also slammed into a AA wall, though not quite as hard with Drew. Will be a young 23 next year so pretty much same things I said about Ward apply to him. Not a top propsect. Not a fader either.
Nick Lee, Ryan Brinley, and Jake Johansen all were in the AFL too but I hate to even note what happens with like 10IP unless it's super special or super bad. It hasn't been. Johansen is an A+ 25yo, a nothing. Lee is unable to throw strikes and almost a nothing. Brinley is the one to keep an eye on but not a top prospect
Anderson Franco - way young (an old 18 last year), way too early to judge.
I guess they do have a decent mix. It's not a great mix, without Giolito being GIOLITO and with Turner now in the majors, I'd be surprised if the Nats were a unanimous Top 10 but top half again? Sure. It's not that the Nats are particularly deep. They don't have a lot of top guys (especially now) who will be definite contributors, or a bulk of toolsy interesting middle tier prospects that could be. It's more like they have exactly the number and type of guys you'd expect to have when poking around a system. So they do have some flexibility to trade. I will say because they don't have depth that if they do deal that it would probably gut the system, but I trust Rizzo et al enough to fill it back up to average status if not for 2018 than 2019.
*Remember - season ages based on age on July 1st. So way I look at it is guys with bdays April-June are "young" because they'll spend a chunk of season at a younger age than given. Guys with bdays July-Sept are "old" bc the reverse is true. Lucas (July 14th), for example, will spend almost half of next year as a 23 year old. Other birthdays I don't use an adjective. This is more important the younger you are.