since there's no invincibility on wake-up, it's no shoryuken, and 1 frame mid-way on a high commitment move doesn't real help it stuff much (as in, in cases where upb does hit something, chances are that would occur regardless of the invincibility).
i think giving the ability for upb to actually trade hits would allow marth a situation where he would receive a trade in his favor advantage-wise. the sweetspot hitbox is so massive that it's unlikely a trade wouldn't occur (if it doesn't occur and you win, more power to marth; if you get stuffed for some reason, there's a high likelihood that under the current conditions, "vanilla" marth would still lose out, if you trade, the knockback is usually high enough that you win frame advantage).
however, i do admit it's difficult to see how such a change would affect him as the 1-frame invincibility is so subtle that i never stop and think (huh, this one-frame is really useful for me, especially in situation x, y, etc. or it helped me stuff edgeguard attempt z or w/e). it's a little harder to imagine considering all the nuances one has to consider, compared to say "hey let's give marth his brawl dolphin slash so he has a legit wake-up option and stuff nearly all frame traps").
i think giving the ability for upb to actually trade hits would allow marth a situation where he would receive a trade in his favor advantage-wise. the sweetspot hitbox is so massive that it's unlikely a trade wouldn't occur (if it doesn't occur and you win, more power to marth; if you get stuffed for some reason, there's a high likelihood that under the current conditions, "vanilla" marth would still lose out, if you trade, the knockback is usually high enough that you win frame advantage).
however, i do admit it's difficult to see how such a change would affect him as the 1-frame invincibility is so subtle that i never stop and think (huh, this one-frame is really useful for me, especially in situation x, y, etc. or it helped me stuff edgeguard attempt z or w/e). it's a little harder to imagine considering all the nuances one has to consider, compared to say "hey let's give marth his brawl dolphin slash so he has a legit wake-up option and stuff nearly all frame traps").