To answer what I know; whilst the Avant features a 4K panel, it also has other technical advantages that enhance picture quality, specifically the ability to measure room brightness and to set the TV accordingly. This is due to having a lightly enhanced version of the BeoSystem 4 chassis. Part of this also includes updated HDMI 2.0 (1-5) ports and specifically port 1 for HDCP 2.2 - this bit is important for the new boxes that are coming.
You are right, they share the same software which has been the single biggest piece of progress B&O has made this past 4-5 years and the same approach in the speakers as well now; Essence, A9, A6, Beosound 35 etc.
Future proofed may be an over expectation, but get an Avant and you will likely enjoy several years without worrying whether you can plug into the latest services or external boxes which is the main thing. I'm sure you'll hear about other technologies like HDR etc, but the key thing is to time-in with where the box providers are going to settle and we are now clear on that with Sky having declared their specs. All of us are good on HDMI 1.4 for now, with an anticipated update to HDMI 2.0 in the future which is covered by the Avant (and I don't believe the 11 does.) As regards things like HDR, its for the 1% who'll watch the best content from a 4K Blu-Ray. I watch streamed movies and Sky, so its irrelevant to me for the next 3-4 years at least by which time my Avant will be reaching almost 6-years old.
The only thing we B&O users need worry about is Bluetooth support for Sky Q which does need Struer to think about an update to their PUC system to extend beyond IR into Bluetooth control.