I tried to enable telnet service but it failed (yes there are some kind of nostalgic men that still use telnet ;-)
ie:
set service telnet
commit
[ service telnet ]
telnetd: applet not found
This seems because busybox doesn't have compiled telnetd applet.
/bin/busybox telnetd
telnetd: applet not found
Tested on:
vyos-999.201710022137-amd64.iso
Thanks.