With the addition of the new exhaust offset property and the colour change stuff, I think it would be cool to add a way to have multiple exhaust meshes on one engine. This could be achieved via XML or the tinker panel. The reason for this is that people like CardZ are already using the new features to do stuff like this:
which results in a much better looking plume, however the problem is that for each additional plume needed to achieve those effects, another engine must be placed, which results in various issues including driving up the part count and having extra thrust be produced when it isn't wanted.
This will not be a thing, but we are working on properties to achieve the same effect with a single mesh, so we're going to consider this as equivalent.