I played at fullerton lan and watched a bit of the cup over the weekend so my thoughts are coming from that perspective.
I really like the threat of a round reset being on the cards as it puts a huge impetus on the attacking team to do something at all times, especially on last pushes. Something I liked about 3 min timer is that round resets happened often on last, as I think that if you fuck up a last push enough times it deserves to go to another mid. However, I do share the sentiment that 3 mins was too short because you would get scenarios like:
Attacking team gets takes second after a scrappy fight where both teams lose players, they wait for their spawns.
After their spawns get there, attacking team gets buffed up, does a double sac and successfully gets a force.
They wait for their spawns to come back in so they can fight 6v6, but by that time they have like 20s left to push.
I think that probably only 1 extra minute would prevent this from ever happening- so a 4 min round timer. 5 obviously offers this too, but you'll get longer stalemates and round resets are less of an option.
I also really like the continuous OT thing. I completely disagree with the sentiment that if you're up like 4-1 at the 30 minute mark you "deserve" to win. I've seen lots matches where momentum completely shifts at the end as one team works out what they need to do to win and they just don't have enough time for a comeback. If you get 5-4ed from that position you deserve to get 5-4ed. I think we'll see this happen more too with this ruleset because people aren't psychologically crushed by knowing that they mathematically can't win.
I also think that the average length of 40-45 minutes is much more natural for a TF2 game. For bo1 30 mins always felt too short to me and for bo3 an hour felt like a nightmare amount of time. I do think DrHappiness' concern is an important one though, there's definitely going to be a scenario somewhere down the line where two teams shit the bed pushing last for 90 minutes at a lan and delay the whole event and hold everyone else up. Not sure how this can be rectified but lan scheduling is almost never on time as is and TF2 has been kicked out of spaces even for things running over with golden caps.