Is it possible to configure (say) faders 1 to 10 which carry subs 1-10 with recorded fade times and using Bump as the "Go" button so that if I bring in (say) fader 4 this way then any other active fader between 1 and 10 automatically goes down to

This is technically possible with sACN show control actions. Here's a quick demo: 

However, i do NOT recommend this. Because storing values, that control faders onto faders, that control values, that control faders, that control values, that control faders, (i hope you see where I'm going :D ) isnt a great idea if you want stuff to work predictably.

if those subs controls the same channels/ parameters, you could use the setting release when stomped.

If not not you could use macros. So sub 1 execute macro 1. Macro 1 does release subs 2-10 and so on.

I would do macro's as well. Make sure to set the subs dwell time to HOLD. Then you should also not release the sub, but bump the sub once more to make sure it fades down at the programmed time.

What I have done, which seems to work, is to set unused channels on each sub at O (not "off") and then select LTP in the submaster options. Initially I had set them to 1% so they were electrically "on", then thought why not 0%, and it worked. I am using an incandescent rig and realise that with leds and/or movers then this may not work. Also the whole show is being busked off the subs/faders so no memories involved.