To be honest, FireMonkey did not interest me much because of the fact that it is not compatible with any VCL application - says the documentation - actually that's not the truth!
To keep the long story short: You can have both in one! (Disclaimer: I did only a few tests and it worked all fine - actually I have no clue if somewhere it's incompatible but I leave that as an exercise to you).
Just create a new FireMonkey form (2D or 3D, doesn't matter) save it and then add it to your VCL application (just accept the warning). You can create your FMX form instance somewhere and just show it - no problem. But what if you want to create some nice control with animations or something and embed it into your existing VCL form? Well, put a TPanel on your VCL form and include the brandnew unit DSharp.Windows.FMXAdapter.pas after the Vcl.ExtCtrls. Then just create your FMX form somewhere and assign it to the new Form property of your Panel - and boom, there you go.
As I said, I just came up with this and it's mostly untested - but that's the case for FireMonkey anyway, isn't it? So I thought this may be very interesting for a few people - especially those that used VGScene before. So have fun creating your shiny and new FMX forms and use them in your existing VCL apps. ;)