I wouldn't say gimmicky, but I am aware the stoneborn keystone offers slightly less lane presence than thunderlords or fervors. But that's just laning phase alone -- my playstyle is more concerned with how my Teemo is going to scale into late game. In my opinion, if the Teemo player knows the lane matchup well, he should be able to have no problems winning and/or surviving laning phase regardless of keystones. I guess it's just up to preference, but I've really been digging the stoneborn + knight's vow combo which has been invaluable in team fights so long as I'm able to provide the necessary peels for my carry. Even if the stoneborn and kngiht's vow effects are halved for ranged champions, every number counts and could make or break a champion's survival.
As for the full tank support Ashe comment, ehhh it's not quite the same as a Teemo with the build stated. All of the items in the build synergize with Teemo's kit altogether: black cleaver and wit's end (armor and MR shred --> Teemo's AD damage from his AAs and the magic damage from his E and other spells), frozen mallet (slows and procs stoneborn), and runaan's (procs Teemo's E and other on-hit). This build really does a great job in providing good damage while also supporting the rest of the team.
I currently just started ranking up a fresh account today and have seen great results so far. This tankmo build does NOT sacrifice damage at all as seen in my matches. I've consistently dealt the highest damage still haha.
https://na.op.gg/summoner/userName=oraque
If anyone's curious enough to try my take on the tankmo build, trust me you won't regret :)! This build is centered on allowing your carry to survive and deal damage for as long as possible (while you yourself will also being doing the damages on the side :P ).