Doubtful. HTC has released numerous new phones since the Tilt - including some with more features/power - but none of them have had the tilting screen. My guess is that the Tilt was a one-off design and won't be upgraded.
The HTC Touch Pro is about as close as you're likely to get to an upgrade for the Tilt, but they haven't released a NAM 3G version yet (though they have said that they are going to eventually).
Well... I suppose it depends on what you mean by a delay. There's a slight delay on mine when starting an app, but it's not significant. Maybe 1 second, but my laptop takes longer than that to open an new app so I don't really notice it.
If you have a lot of crap stored on the device (instead of on a storage card) then that will definitely slow you down. I have 104 MB of free storage memory and 68 MB of free program memory right now because I store and install EVERYTHING on the storage card. Nothing goes on the device itself if I can help it.
The only rumored software update that I've seen was from back when everyone thought the Touch Pro was going to be tri-band, and the update would allegedly sacrifice the EU 3G frequencies in order to add NAM 850 EDGE to the device.
I haven't seen anything saying that you can hack a Touch Pro to add the NAM 850 band to its 3G support.
I was in an At&t store yesterday getting an iphone for my girlfriend. I saw one of the sales reps walking around with a phone i wasn't sure of what it was. Then when i saw it I asked him if it was the Fuse. He said yes and it should be out within the next few weeks, as early as next week. I've seen it on a few other sites and here. http://www.htcwiki.com/page/HTC+Fuze+for+AT%2 6T?t=anon