Sounds interesting. If I were doing it, I would probably make a vanilla bean pastry cream, subbing yolks for some or all of the whites (2 yolks for each white), reduce the sugar considerably and then use half and half or even light cream instead of milk- all to mimic the heavy cream/ yolk richness of creme brulee. Perhaps the pastry cream in RHC (Bostinis) might be a starting point, it would probably need to be made thicker.
For the caramel, I would take the amount of sugar removed from the pastry cream, multiply it by 1.25 (for a light caramel) or 1.33 (for a dark caramel), and make hard caramel with it. Then I’d pour it onto a silpat/cake ring to create a thin disc of hard caramel the same size and shape as the tiers (or a little smaller). Once that cooled, I’d top a chilled cake layer with a hard caramel disc, then spread that with pastry cream. The hard caramel would be thin and easy to break, but it would probably be fine as long as you fit the pieces back together.
In time, the caramel should soften completely from the moisture in the pastry cream, and since most wedding cakes are made well in advance, that would make a soft caramel layer. The cake layer beneath the caramel would absorb any excess moisture to keep it from getting too liquid. Might need a test cake or two to be sure of timing/texture. Might also be a good idea to let the caramel soften part way before decorating the outside of the cake, so that the cake doesn’t shift as the caramel softens and give you puckered sides.
The other thing you could do would be to make a thick caramel sauce (with cream, butter, vanilla), thickened with gelatin if necessary, and layer it over the pastry cream.
I wouldn’t pair this with anything sweet like a high-ratio cake.