Please consider a VyOS build for x32 ABI - unchanged 64-bit kernel, but using 32-bit pointers in user space means significant reduction in memory usage, fewer cache misses, better performance, while still keeping advantages of 64-bit vs 32-bit like more registers. This limits address space to 4GB per process (whole machine can still have more than 4GB RAM though) which is still more than enough even with multiple full BGP feeds today. Many machines VyOS runs on have <=4GB RAM anyway, in this case imited address space per process doesn't matter at all, but better performance does. More about the unofficial Debian x32 port - https://wiki.debian.org/X32Port

Back in the old days (a few years ago) when working x32 Debian installer was available, I was actually running a small Debian x32 installation with BIRD doing full BGP, on an old machine with just 1GB of RAM (which was not enough for Vyatta back then anymore) and it worked quite well for a year or so (until the hardware physically failed). So it should be reasonably stable, might uncover a few bugs in some software (assumptions about pointer size etc.) though.