OKOK I know you like byler but if you HAD to ship mileven how would you improve it/Headcannons for it?
sorry this took a million years for me to answer
if i were to improve mileven, i'd say wait a little longer before the actual kiss/more romantic stuff starts to happen
i think it would be cute if mikes crush on her from s1 was there and known, but because shes fresh out the lab, she doesn't really get it, and he's too embarrassed to really make any big moves
in s2, i would say make jane come back a little earlier, and give them at least another one-on-one scene, and she has been watching all those romance movies and things, so i think she's starting to piece together that that's what she's feeling for mike!
in s3, i wouldn't make them as attached to one another as they were (because im so sorry but they were so clingy and obsessed w one another it got to the point of being disrespectful to their friends), but i'd want their relationship to certainly develop over that summer, but its really like they're dancing around one another at that point, HOWEVER, they do talk about it in the middle/near the end, and then yeah, BOOM, MILEVEN!!!
as for hcs, I don't really have a ton, and they could be read both as romantic/platonic, but here!!
jane likes to look through old photobooks of mike because mrs wheeler always encourages her too, and even has a couple of pictures of baby mike in her room bc she knows it embarrasses him, AND she just thinks he was very adorable back then
will teaches jane to draw (as you might've seen from my hc answer to your ask), and so she draws her friends, and mike, and would send letters with doodles/drawings of him in it when they would exchange letters from cali
picnics!!! they like to go on picnics together
along with looking at the stars, mike would use what little knowledge he has of them to name the different constellations and junk, jane joined in when she could, but then they'd just end up making their own stuff up