There's an aircraft with all kinds of "Could have been" to it!
I've often been tempted to do up a Javelin with some refinements that were tossed about in the real world, like thin wings. I'd also be inclined to replace all those little vortex generators with a wing fence or two.
I've also read that the horizontal stabiliser was completely superfluous and that it was there due to a poor understanding of delta wing operations and the aircraft could have flown without it, so I'd probably do away with that and put on a thinner vertical fin.
I was also thinking about Mirage type intakes with variable centre bodies and perhaps a bit of area ruling on the fuselage.
More powerful engines go without saying.