If someone was hiding in the house when they got home, where's the evidence to support that?
I'm open to considering IDI (heck, someone on here once made a very persuasive case for JARDI), but I think you have to have more than the DNA. Yes, DNA is persuasive, but the Ramsey's actions following JB's death need to have a plausible explanation. I've not yet seen something that effectively explains their stonewalling, their lying, and other pieces of evidence from the scene which point to them.
I'm not trying to be hostile to your idea at all. Persuade me.

I've got an open mind still on this case, although I lean BDI.