From my perspective there is no hurry. I added libcurl only as fallback for those situations where a site doesn’t support older cipher suites and the site requires https (or the user somehow absolutely wants it). In all other cases libcurl isn’t even used, even with https enabled. Most sites have liberal cipher requirements, but the biggest culprit is Cloudflare free service, which requires the elliptic curve ciphers.
In case of rarbg it’s easy, coz they support http: as well. So, no hurry.
As for the 64b, it runs as 64b on my ubuntu server as well, but that has all the required native libs as separate packages.
The most tricky OS is OSX coz we have to supply some libraries (mediainfo,sqlite) ourselves, which are 32b, so running sonarr on OSX requires 32b mono.
You probably could compile mono 32b for syno, but that could cause issues when other apps expect 64b.
Edit: added GH issue for tracking: