The bittersweet cocoa almond genoise is wonderful and I love it, but it is a dense cake, maybe even denser than a pound cake. And I don’t know if it would work in anything larger than a 9” pan, maybe, maybe not. It is also one of the least sweet cakes in Rose’s repetoire, so may not be a crowd pleaser if your group likes things sweeter.
As regards Gene’s comment to make the custard with tapioca or cassava starch/flour, it definitely works but in my experience you may need to use less to get the texture right- a test batch may be needed.
You could make either chocolate cloud roll or cocoa souffle roll and stack many layers with the custard to get the height you want. Kind of like the RHC chocolate feather bed. Given how much custard that would be, it might be good to lighten it with either meringue or whipped cream. It would be an awful lot of work, though, all those layers!
Annother idea is to make a genoise using gluten free flour (rice, potato, cassava, or a pre-mixed GF blend). But I’ve never tried it so again, a lot of testing may be involved.
I like the idea of either the oblivion or a cheesecake wedding cake. One huge corn and gluten-free custard.