If the 11th gen 10nm core Intel Core is ready now and M1X is ready now it would be odd to just keep selling the 10th gen chips for 4-6 months.
Also this idea that this somehow breaks with what Apple would ever do is silly since they do it all the time and are doing this exact thing with the Mac Pro.
Am I saying 100% they will do it? No because nobody ever knows anything for sure- but it will look silly to keep it on a a very old architecture for half the year. It would hurt sales while they are waiting for the M1x and also look arrogant.
There are going to be some use cases where that new intel CPU with a direct GPU may very well work better for some "pros" and for them they'll want to keep the Intel CPU until the kinks are worked out
Apple has often had long delays between the release of specific Intel processors and the Macs that use them.
Compare these two pages for MacBook Pro releases, and Intel mobile CPUs:
Tech specs for all Apple MacBook Pro from 2006 to the latest. Dates sold, processor type, memory info, storage details, configuration options, model identifiers and more.
everymac.com
Intel® product specifications, features and compatibility quick reference guide and code name decoder. Compare products including processors, desktop boards, server products and networking products.
ark.intel.com
e.g.
MacBook Pro 15" "Core i7" 2.2 Mid-2015 (IG)2.2 GHz Core i7 (I7-4770HQ) - May 19.2015 - 8-11 months later
MacBook Pro 13" "Core i5" 2.0 Late 20162.0 GHz Core i5 (I5-6360U) - Oct 27, 2016 - 13-15 months later
...and so on.
Sure, some Mac releases are in the same quarter as the CPU release (in 2019 Intel 9th & 10th gen Macs were "up to date"), but most lag by more, so the trend clearly shows that Apple is quite happy to release new machines with >6 month-old Intel processors. I've followed Mac releases for over a decade, and it's undeniably true. Read the links I presented and compare.
Admittedly, if Apple leaves the Intel 9th Generation CPUs in the MBP16 (released Q2'19) it would be an unusually long gap between updates for the MBP15/16 (but not other Macs), but given the fact the CPU was already a year old when they put in to the June 2020 MBP16s, and the fact that Apple are moving away from Intel, I'm really not convinced that they would bother to update it to an 11th-gen Intel if there were only 4 months (+/- a couple of months) for them to release an Apple Silicon variant that would greatly surpass it.
Even if this is technically possible, and would be good for a small subset of users who need to ensure legacy compatibility, it would send a terrible message to stock-holders for Apple to say "hey, I know we said that we're migrating to Apple Silicon, but our new flag-ship laptop is going to have a great Intel CPU, because we're not quite ready....". Imagine the effect on stock-price! It won't happen because of this. The negative press of people like us whining because the MBP16 hasn't been updated for 2 years is tiny in comparison...