Also very interested in this. Ready and willing to test.

Another willing to test.

Not had a lot of time recently, but I have kind of been waiting for the configuration nodes to be ported to Python, so that this can be written in the new / modern way.

Now that this is mostly done, I suspect that it wouldn't be too hard to implement - copying a different PPP based module as a starting point.

It looks like xl2tpd is available in Debian, so won't need packaging separately:
https://packages.debian.org/stable/xl2tpd

And it looks like the Kernel modules exist in my VyOS kernel (VyOS 1.3-rolling-202006110117):

vyos@vyos:~$ grep 'L2TP' /boot/config-4.19.125-amd64-vyos 
CONFIG_NETFILTER_XT_MATCH_L2TP=m
CONFIG_L2TP=m
CONFIG_L2TP_DEBUGFS=m
CONFIG_L2TP_V3=y
CONFIG_L2TP_IP=m
CONFIG_L2TP_ETH=m
CONFIG_PPPOL2TP=m

Have you had any time to look into this more? I am at a point of wanting to migrate off a Mikrotik RouterOS virtualized instance to a piece of hardware and would love to move to VyOS at the same time.

Willing to test anything that might be needed in order to help move this along.

Should I hold out any hope for this to be implemented? Still willing to help test and do whatever I can to get this in.

I have a couple of routed public /29's which do not need encryption, as they are just internet crossing data anyway, and would like to use VyOS as a central router for all my connectivity before splitting out into the network.

Just adding my +1 for this feature, would be very useful.
If I get time in the coming weeks/months I will try and pick up on the analysis where @njh left off.