The TodoDekuBaku threesome is interesting. I'm huge Tododeku shipper and slight Katsudeku shipper but really not a Todobaku fan. Those two just don't mesh... That doesn't stop the polyamorous relationship from working though, since not all members must be involved with one another. I could see it working with gray-ace/demi Shouto having a primarily romantic relationship with Izuku (with the occasional tender "lovemaking") while aromantic Bakugou has more of a physical relationship with him.
Whoa I’m late to answering this, but better late than never!
The TodoDekuBaku ship is quite interesting and I’m glad you think so! I feel you with being a Tododeku shipper and slight Katsudeku shipper with not much of a Todobaku fan, which is cool! To each their own, I say.
For me, I ship them both too hard and too equally, so then this happened.
I also just ended up shipping Todobaku ever since their fight in the Sports Festival and during the (spoiler if you don’t read the manga-during the School Trip Arc.)
The way you describe their dynamics is a fun one. I can totally see what you proposed happening within their relationship.
I have this headcanon that Bakugou Katsuki is secretly a sweetheart underneath all those emotional walls he has, so as soon as he gets more confident emotionally, things may change, but just a little since he is Bakugou Katsuki (lol love this boy). And for me Todoroki Shouto, I agree with the romance with him since I see him taking it slow, a cautious dude overall with such things.
But that’s the fun of shipping! Anything can happen, especially for this dynamic trio of baby heroes.