Before sleeves suits became popular I used to wear it on the run. I’ve worn it in a half-Ironman. Castelli actually noticed athletes doing this and created a sleeved tri suit using the T1 Stealth

https://www.castelli-cycling.com/...its/p/861810418P-010

ALL OUT SPEED SUIT
IT SHOULDN'T BE A SURPRISE
When we originally designed the T1:Stealth top we imagined it being put on in T1 and coming off in T2. Then we saw swimming and running in it. Marino Vanhoenacker was the first one to ask for a Sanremo style suit with the T1:Stealth upper part. He helped us work through the development phase, then debuted it at IM Kagenfurt for his 8th victory in that race. This suit is no-compromise speed equipment. It's not the most flexible for the swim, nor the coolest in the run. But if all-out speed is what you want, then you want this suit.

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I swim in it (unzipped almost all the way), then wear it on the bike, then take it off for the run (have sleevless tri-suit below it).

But I am thinking about doing what you're talking about and just wearing tri shorts, and T1. I feel it's kind of restrictive and I don't like sleeves on the run, so if I go that route I'll probably ditch the T1 for the run and throw on a tank top or the castelli run top that TO asked them to make.

I have worn it for the run on two ironmans, both hot races without a problem. I have also worn it over a tri top and removed it in T2.

I typically leave it unzipped under my swim skin and wetsuit.