3B?
Why not try him out as a reliever?
There is a logic to trying Swihart at third base given our lack of depth at that position. It's a judgment call, and comes down to your assessment of which of Swihart and Vazquez is most likely to become our starting catcher going forward, and what that means for the other one.
If you think Swihart is our starter in 2018, then the thing to do is to either keep playing him and let him learn on the job, in which case you either leave Vazquez in AAA where he has no business being or DFA Hanigan, or you send him down to AAA to let him refine his defensive skills in a lower-stress environment and run Hanigan and Vazquez for the next few months, and make decisions as the season goes on about how well that's working and whether moving Swihart back onto the 25 man at the expense of one or the other two constitutes an upgrade.
Or if you see Vazquez as the starter, the thing to do is to demote Swihart and either commit to him full time as a catcher and potential platoon partner or trade chip, or explore Swihart's athleticism and see if you can increase his utility to the team, or his value in a trade, by trying out 1b, 3B and maybe a little outfield, I don't think there's a reasonable doubt that Swihart has the athleticism to play on the corners if that's the team's judgment call. The question is simply one of whether you might consider Swihart "blocked" at catcher if Vazquez is successful at making the job his own.
It should be noted that I don't believe the team has ever committed to Swihart as its starting catcher of the future. Vazquez, on the other hand, was the intended starting catcher last year. IIRC, Swihart got the job only after Hanigan and Vazquez both got hurt.
Lauber even brought up the concept of carrying 3 catchers (at the expense of Sandoval). It's not 100% insane. Swihart could learn from the other 2 and at the same time offer offense off the bench. Who knows how many games Vazquez will be able to catch?
IMHO, it's only not insane if at least one of them has some confirmed utility outside the catcher's spot.
The times I've seen that tried, it was because the team had either a 1B or a backup 1B with catching experience and could spell the 2 catchers at need. So it wasn't so much three catchers as a three man catching depth chart on the 25 man roster. I don't know that I've ever been aware of a team actually carrying 3 men on its roster that were all strictly catchers with no other utility.