There aren't that much of trademarks/copyrights.
In the UDK version, maybe, but UT3 stands under Midway's copyright. Moving their assets or code to UDK pretty clearly breaks the EULA. If someone would sue you or if noone gives a dime as long as you don't commercialize a game, that is an other topic.
But even with such permission, all the native code where noone knows what exactly Epic does there... you'd have to rewrite a lot yourself, don't know how meaningful that would be. By the way, what improvements for UT3 do you expect from UDK over the Engine of UT3?
And i doubt UE4 will work for Arena-FPS players. Have you checked the system specs? You won't get that much of performance on low end PCs.
You reffer to the
recommended specs for the
Editor, or to the
minimum specs for running a
game?
UE4 is supposed to scale well, like that elemental demo: high quality details on a PC and less particles and details on a (beta-PS4) console.
Even mobile phones will run UE4.
Epic also wants to rule the browser game segment with javascript-UE4 games, they can't expect high end machines playing casual games. ...and Epic will copy your facebook profile pic and gather data about your friends, no joke... and pass data about you to a set of trusted companies, but no need to tell which those are. Murica is proud of you.
So, back to topic, the min specs will very between different games, which does not exclude arena FPS on UE4. ...And the Editor will be improved, Epic clearly states the current version is only for early adopters.
If games will run 60 FPS in 720p or 1080p on a Xbox 1 or PS4, that may already set the maximum of the graphics quality bar until the next console generation is there, I guess.