Using plain or flavored meringue for cake filling.

Do you mean using it uncooked? It would collapse after a while, so I wouldn't use it as a filling. And I don't think it would take the weight of a cake on top of it as well, even with a dam.
 

I agree, you can always add caramel to a swiss meringue buttercream? You can make it with brown sugar as well.

Adding caramel to a cooked meringue does work. Cooked meringues are the base for semi-freddo's and they freeze very well.

Personally, I like to add a caramel to whipped cream as a filling. The benefit is you cut back on the amount of sugar you use in the whipped cream so the filling isn't overly sweet.

To do this: first whip your cream until stiff, then in your mixer add the caramel to taste.

Even leaving it slightly under mixed is great, it's like a caramel swirl.

It would totally work as long as you made it into a "marshmallow fluff", or basically a really soft marshmallow by adding gelatin into the cooked meringue.  There is a French name for this type of filling, but I can't for the life of me remember what it is, or maybe it's the name of the type of cake with the marshmallow fluff layer in it?  I think it also has a layer of sponge, a macaron disk and maybe a layer of nougat all in the cake?    Anyway you make a circle on a piece of parchment and pipe the fluff in the size you need, let it set up a bit them flip it right onto your cake layer.  The outside would somewhat firm up but would be gooey when you cut it.  You could add all sorts of yummy bits into it like candy, nuts, dried fruit, chocolate etc. It won't deflate and depending on how gooey you make your fluff, very durable.

Hi, i make brown sugar smbc and add jodie foster's caramel recipe(on this site) at the end(caramel is cooled) It is delicious. I use for filling . You can just make the vaniall smbc and do the same. It will be delicious. I do it all the time. hth

I was thinking that an italian meringue buttercream with caramel to taste would be a good idea as it holds up well and tastes awesome!

Do you mean SMB without out adding the butter? or with it? Because I add home made caramel sauce or dulce de leche to my SMB all the time! It's soooo yummy. I don't make SMB without it!

Then a cooked meringue with caramel might make the cut! :D