Presumed Plan : Anthony Rendon will continue to start at 3rd base. Frandsen will likely back-up.
Reasoning on Presumed Plan : Anthony Rendon is an outside candidate for MVP. There is very little he can't do on a diamond. Along with some top-notch fielding at 3rd base (he's in the discussion for best defensive 3rd baseman in the NL), Anthony can :
Hit for average : His .287 average was 20th in the NL
Get on base : His 8.5% walk rate may not seem great but in this new world it's good enough for 27th in the NL. That added to his average gave him the 20th best OBP in the league.
Hit for power : His .186 isoSLG was 14th in the NL
Run the bases : His 17 SBs was 17th in the NL. His baserunning ranked 2nd. His "speed" stat was 8th.
It is difficult to find a flaw in his game and he'll only turn 25 next year meaning he's likely to be at least this good for another 5 years and he might get better. There is no question that Rendon starts on this team, or any team for that matter.
Frandsen? He is capable of playing 3rd base and hitting a baseball occasionally. He is also signed next year and a scrappy vet.
Problems with Presumed Plan : Ok, we got to be picky here. But I suppose you could say the Nats are relying a lot on one season of stats. Sure he did well in the minors but in a big chunk of season in 2013 he was merely ok. So perhaps we caught his best year in 2014. While he fields well at 3rd he isn't the defensive whiz that Zimmerman was during his prime. And while he does everything very well, he hasn't yet shown himself to do anything great and quite possibly won't ever reach that level. Is he going to hit .325+ or 35+ homers? I can see it happening but I'd bet on "no".
Really though the biggest problem is the one noted previously. Rendon can play other positions and there are actually some decent 3rd base options out there which doesn't always happen, so it might be better to shift Rendon over.
Frandsen. Eh. Where Rendon does everything very well Frandsen does nothing very well. Actually, that's not entirely fair. He does make contact well. But he doesn't get on base, he doesn't hit for power, he's not a good fielder, he's not a good baserunner. Bench players are inherently flawed but you like someone who's major strength is more than "Might not strike out and by putting the ball in play could get a single"
My take : This really isn't something to mull over. Could it be a fluke year? I guess. But even if you split the difference between his first two seasons he's a good starter. No he's not a great 3rd baseman with the glove, but he could be the best currently in the senior circuit. How is that an issue? And the fact that he may not reach superstardom? That's ok. I think we'll all take 5 more years of plain old regular stardom. Rendon is a cornerstone of this franchise in his 2nd year and projects to be straight into the next playoff cycle. At worst he's a good dependable starter at typically a difficult position to fill. At best he's a perennial All-Star and wins at least one MVP.
I don't like Frandsen but who better is out there? If Rizzo is smart he makes a courtesy call to Eric Chavez to see if he's reconsidering retirement, otherwise shrug your shoulders, I guess. See if you can't draft someone? Really I don't know.
Outside the Box Suggestion : We've already covered a shift to 2nd so let's think of a different OTB suggestion. Rendon is a cornerstone for the Nats right? A guy you desperately need to keep healthy and happy over the next 5 years and maybe beyond. While he hasn't had a major injury in a couple years he did have them in 2009 and 2010 and 2011 and 2012 (ankle, ankle, shoulder, ankle). The shoulder one in particular forced him to DH most of his last year at Rice. The last thing the Nats need is another guy they are looking to move around to accommodate because of injury. So why not move Rendon to first right now while there is a hole? Make him your first baseman and never worry again about where he might play if he gets injured. Set him and forget him. If you think it's stupid because he's such a good third baseman, lets remind you again that Zimm was a GREAT 3rd baseman, fair to make comparisons to the best ever. Seriously. That good. One injury later and he's stuck at first.
Filling 3rd won't be that much of an issue. We've noted there is a rare... well I wouldn't say glut... but multiple decent FA and trade possibilities at 3rd this year. Rizzo would find a way. The real issue would be what to do with Zimm. My plan would be to super sub him around the diamond. LF, 2B, occasionally 3B. Really the goal would be to make sure he gets consistent at bats because you are showcasing him for a trade to the AL where he can DH. Then do that when you have a chance.