Yes, the intention is to only install x64 TCMD v20 on x64 Windows. Installing x86 TMCD on x64 Windows has always been an enormous support PITA, as I get endless "bug" reports from people saying that TCMD is running the wrong (i.e., x86) version of Windows utilities, and is writing to the wrong (i.e., WOW64) registry entries.
As x86 Windows is currently running < 2% of TCMD installs, I'm not particularly concerned about the very rare cases (i.e., plugin developers) who might want to test x86 TCMD on x64 Windows. If you really want to run x86 TCMD on Windows x64, use TCMD v19. And don't expect your test results to be particularly meaningful or valid.
I will be dropping x86 support completely in the next version or two.