Yeah, Via doesn’t have tapdance. Whereas Vial does have tapdance, plus combos, key overrides, and a range of qmk settings. I use Vial on my 15 button mouse, where I couldn’t even live without tapdance anymore.
You could enter your tapdances directly into qmk, but having it available in a GUI is much nicer.
For LSPO, you mean Space Cadet- Left Shift, Parenthesis Open? Haven’t used it myself, but Vial is supposed to support it https://github.com/vial-kb/vial-qmk/blob/vial/docs/feature_space_cadet.md, and tapdance can also do it.
Do you mean, like, sideloading a draft keyboard definition in Via? I’m afraid more is needed for Vial. Porting guide - Vial
Which keyboards were you looking to do? ANSI, ISO, keypad, macropad?
I made an ANSI vial layout .json which you could use, so you don’t have to do that part of the porting at least. Feature Request: Num Lock on boot, Schematics for Keyboards (to build vial support) - #7 by MJ1
Now, Framework has made a few changes in their QMK fork that you should bring over to a Vial build, but I don’t know how many are absolutely necessary. For example, there is Airplane mode button support which Framework added, but if you don’t use that, then you might not bother bringing it over.