I ate mayo maybe a few times in my first decades
I still hate mayo
Though I liked when I made it with lard (I dislike olive oil and lard is way cheaper anyway) and the yolk overpowered it (10g lard for one yolk, I think)… I still never made it again but I have to avoid added fat, I overeat fat without its “help”. And even my mayo was just too fatty.
The bread sounds… Interesting and probably not very good for me, dry and tasteless to my liking but such things can helped (I clearly would add yolks, all my bread must have them but I am a maniac if it’s about yolks :D)… But it looks good and fluffy and well, if it’s just a base so I can add much more fat later… I would try it out but I don’t ever buy egg white protein as I am very choosy about the source of my eggs… Maybe I could replace it with something… I have some other protein powder I can’t do much with…
I always make cheesy egg white thingies in my muffin mold when I have many eggs (whipped egg whites, tiny salt, some grated cheese. barely anything but the original recipe had a lot). My SO loves it even after eating it almost every week since years but he is a weirdo. It’s boring to me. But edible when one is hungry and some sausage makes it WAY better 
My marshmallow uses egg whites too but well, it’s candy (and not really marshmallow, I obviously put yolks in it as it’s very tasteless without it, no matter the flavorings. I can’t really eat no-fat stuff either). It helps that I almost never ate marshmallow in my life (only fruits could get away with being not fatty)… It’s quite nice when making right, I got the recipe from the Internet, many keto marshmallow recipes use egg whites.
Hungry me can just fry and eat them too but it’s not the best. Nice but well, I prefer my scrambled eggs having more yolks and whites if possible, not less. It’s the same for sponge cakes, angelcake is plain bad to me. (My sponge cakes are 100% eggs.)
But normal mayo (doesn’t matter if keto, I mean one yolk for a ton of fat) has so little yolks. One egg white is easy to use up!
I would love to figure out how to make an egg white into the same wonderfulness that is boiled egg white. Boiled eggs are special, I almost always eat them with twice as much egg whites as yolks (and it makes the problem of leftover dry yolks but I have many ideas for it, first of all, deviled eggs fillings, they don’t need to put into egg whites). But only boiled eggs have that wonderful whites. Maybe poaching the whites in some nice broth are nice too?
Sometimes I combine my two “leftover problems” and use egg whites with boiled egg yolks. I made recipes like that. Especially useful for my carnivore baked things where the egg yolk is used as dry stuff. I don’t have any clearly good one though.