Note: not trying to change or argue with TNet's direction - I feel it probably is better suited to TCP as well, but onto the discussion:
Sounds very awesome! Regarding UDP, there's a solid open source UDP here:
http://enet.bespin.org/As for first packet being lost via UDP - as you know if TCP has been in use heavily by the system, there is proof online that a computer using TCP will cause a higher rate of UDP traffic to drop. So you're authenticating, you're setting up a users, or a chrome browser is refreshing, or twitter client is refreshing, or any number of things on a typical system will cause that first UDP packet to fail a lot more than normal - something like 5% to any%. This means doing a single test for UDP then telling the system to be TCP only isn't a very good move overall. But that's only a bad move if the system really should support UDP.
Regarding photon latencies, I found europe tests and US tests (respectively) to be within the 40ms range. This is slower than TNet which saved 10ms on average (not worth worrying about in terms of difference). People will need to run a server somewhere that manages traffic. This is what Photon cloud does. So performance wise, I don't really see much of a difference if you want the game to continue after a host quits. I don't think currently, it's vital for a user to host the relay server, in fact it means more dropped games at this point.
The main point of contention is Photon can get expensive, and I think this is the valid reason TNet is so appealing

I agree with today's internet, TCP is much better than it used to be though.
If I'm running on consoles, I don't have a nat punch through issue, but I do have an issue where users might switch off their machines suddenly so it boils down to if I want to use azure or leaseweb to host the relay server or pay Photon to do it. In fact I was surprised and pleased that TNet was so full featured so early on vs say, Photon. TNet is 10x easier as well.
That's my current thoughts about it.