Today I've completed version 0.4.0 of the Birthright 5E conversion document. You can find it here.
I've added conversions for all core rule book realm spells and plan to add a few more of my own design. I reviewed a number of the ones from the Book of Magecraft and the Book of Priestcraft and found them unsuitable for my conversion purposes -- many of them introduce additional crunch into an already mechanics-heavy bolt-on for 5th Edition, and I wasn't too keen on making this even more impenetrable for those who want to use it.
It's also approaching a whopping 100 pages. Yowza!
Hope it's useful for people, and I'd love to hear any about any feedback or bugs you might find in it. I haven't had the opportunity to get a group together to playtest any of it, particularly the quick battle-resolution mechanics. If anything seems obtuse or irrelevant, I'd like to hear your thoughts on it.
As always, I don't intend to package this (or anything else I convert) up for sale on the DM's Guild for obvious reasons. Enjoy it!