Syslinux is newer and works at-least-as-well as lilo which is also documented in the handbooks. (less static references, so, for example, I've successfully ghosted a drive from one computer to another and still had it boot with SYSLINUX, but not with lilo) Moreover, many people that perfered lilo long ago are now migrating to syslinux, meaning that giving information on how to install it (which isn't that long, to be honest) would be benefitial to those users as well. I'd submit a patch, but up to now I still have no idea unto how the handbooks' source looks like, and wouldn't want to submit a patch (e.g. in HTML) that wouldn't be useful to anyone. I'm not sure unto the other handbooks, but x86_64 and x86 both should get this change.
I don't know if switching the handbooks from LILO to syslinux is an improvement, but I'm not opposed to the change. However, the current syslinux page on the wiki (https://wiki.gentoo.org/wiki/Syslinux) does look a bit more complex than what LILO does. Most likely because syslinux can do more, but I don't know how to document the use of syslinux as a boot loader. Can you draft up how you'd like to see it on the handbook in your user profile on the wiki? We can then look at the content and see if this can be moved forward or not, or at least if we can then update the syslinux documentation and refer to that (I'd like to make the instructions more static and refer to the various options as separate articles, but like I mentioned switching one option with another is also doable for me).
grub2 is used everywhere; switching to syslinux for all our handbooks doesn't seem feasible. if someone wants to do an up-to-date syslinux page, let us know. otherwise, closing.