Xiaomi Router 7000 - Thoughts

a) still no 6 GHz support
b) new SOC, which is still only starting to get partial mainline support
c) too early to tell, expect years (plural) until it may get supported
d) don't expect 802.11be support to be retrofitted, even if that were possible (the standard is not final yet, so no way to tell), especially Xiaomi is extremely bad at keeping their firmware maintained for security issues - let alone adding new features (if the ax3600 is anything to go by).
e) 802.11be without 6 GHz support is a bit…

If you're looking for a new device, get one that is supported in OpenWrt right now - if you're adventurous and willing to do some development yourself, at least a SOC that is already fully supported (there are ipq8074a based devices with 6 GHz radios[0], [1], not supported by OpenWrt yet, but reasonably supportable if someone with the hardware would work on it). It doesn't make sense to place any bets on new SOCs, until 'someone' has at least some kind of proof of concept OpenWrt port running (not QSDK, but a mostly clean OpenWrt'ish kernel).

Reminder: it took well over 4 years (from initial device availability), before ipq807x support could be merged into OpenWrt/master.

would be interesting -fully supported- options right now, around half of your prospected price of the Xiaomi 7000.

[0] not cheap.
[1] the Verizon CR1000A would be another example, albeit a little hampered by its Realtek rtl93xx switch.