What I'd like for an engineer. No really, read on, this time I'm serious.
What I'd like for an engineer is a weapon unlock, that heals all of your stuff remotely, but only while you are doing damage with this weapon. Hear me out. The main problem is, when you put up your stuff, you can't move away for 10 seconds because you can be pretty sure it will go down.
Now let's say you CAN go away and shoot at people. And while you are away and shoot people, you buildings get the same amount of damage repaired as you've just dealt with this special weapon.
This fixes several problems:
- Turtling. It is more likely to find a sentry or whatever without an engineer babysitting it
- Reward for leaving your stuff (points and building repair)
- Getting the engineer out of the danger zone (being able to fix your stuff without being in the danger area and dying first)
- Being able to repair everything at once without having to put everything in your immediate area
And the downsides are:
- You have to actually deal damage to someone, if the sentry is under a heavy attack (uber or similar), it's just as unlikely that your stuff survives as before, unless you are actively dealing damage
- When engaging a target you obviously risk dying and not being able to repair anything until you respawn
- There is still a sapper, which i'm unsure of how to deal with it. If you make it unaffected by this weapon, people will keep on turtling, if you make it destroy sappers, spies will be at a big disadvantage. I'm thinking, make the sentry being repaired, without destroying the sapper (and while staying offline obv.). This way you still have a chance to get back to your stuff as long as you deal damage on your way there and a spy has a good chance of taking out the buildings or the engineer without having to replace the sapper.
Another idea would be a metal conventer, which does pretty much the same, but when you pick up metal (boxes, weapons, building debries). Same concept, but a bit more reliable, as you know where to get metal usually and don't need to be in danger.
Another idea would be a teleporter for your buildings. Basically, you put a building somewhere, then go somewhere else and place a beacon or something (might need to keep pointing it at a small area for it to activate), then one of your buildings of your choice gets teleported to the position of a beacon (preferably not instantly)

This could help with the second problem of engineer, having to move your stuff constantly and having to rebuild it over and over again.