I think it would be thick and slippery enough but I'm not sure how easy it would be to make enough for a whole session.

Saliva dries out much too quickly for me when used even vaginally where it has help from natural lubrication so I don't see how it could have any kind of success anally. To start, sure, but it's not very practical for a whole session.
I guess the main positive feature would be that it doesn't get sticky? Hm

Honestly.. Saliva isn't the "best" lube, but it's the main thing I've used with anal sex. Now that I own lube (never did before joining Eden) I'll use it during anal sex unless it's sponatenous anal. But before, spit or shower water was the all that we used. And it did hurt sometimes a lot, but as I've gotten older I always try to make sure it's well lubricated with spit or whatever we were using.
So saliva isn't perfect and doesn't last... but I've used it. It's been fine as long as there's enough of it and my guy spits more during the sex so it stays slick.

I don't think saliva makes good lube at all, at least not for situations like anal. I can't imagine it being thick enough or slick enough, and I certainly don't imagine it would last an entire session. Plus, I don't like the idea of being spit on, so it just seems distasteful to me. YMMV, of course.

One of my mentors mentioned to me that there is more bacteria in spit than on your average toilet seat. Ever since then spit for lube has been stomach curdling to me.

I've used it in the past, and it's worked a bit, but it doesn't work as well as actual lube.