Is tank Shaco possible?

Anything is possible, but whether or not is good is the real question.

Yes. I once went tanko in an aram game because all of us were squishy glass canons. I wouldn't work on sr though, there's nowhere a tank shaco would be able to work unless you transitioned from an early damage dealer to a late game tank.

You're just wasting all his assassinating potential, and he really doesn't have strong CC to cover the team.

It's more like "Fighter" Shaco.

Shaco is not Braum or even Cho'Gath; he lacks the defensive utility to actually do anything, well, defensive about any defensive items he invests into.

That said, Fighter Shaco is certainly a possibility. Shaco tends to fall off hard late game anyway unless he's building like a true carry (a role in which he falters in), so supplementing Shaco with defensive items can turn him into a sort of "front line fighter" or "tanky diver" and actually give him a good role for late game team fights without getting blown up immediately.