I think that's for the best. RtP can stand on its own legs and the cameos, while cute, are really more a distraction, as opposed to advancing the narrative.
Fun, but too much of anything is not a good thing.
Well, yes, too much is, by definition,
too much. But exactly how much is too much is always a lot harder to define.
The cameos are novel, and novelty is a good thing when it is still rare enough to be novel. The rarity is more about the number of people/games doing it, than how many in one game.
Did you ever watch "The Usual Suspects", one of my all-time favourite movies? It is absolutely packed full of references to other stories.
For a start, the title itself is a reference to the classic movie Casablanca, in which the cop says "round up the usual suspects" a couple of times for when they are creating a fake line-up - perfect reference, and a little nod to real movie fans that shows an appreciation for the artform itself.
Then there's the lawyer in it, played by Pete Postlethwaite, but the name of the lawyer is Kobayashi - another reference, this time to the infamous Star Trek storyline of The Kobayashi Maru - an unwinnable situation.
There's plenty of others, not least the "Elvis has left the building"line. All those little references are there to reward and acknowledge the viewer, a nod of recognition to shared culture references and tastes.
Ever watch "Reservoir Dogs"? Did you spot that the threeway gun faceoff in it is a direct reference to the classic spaghetti western "The Good, the bad, and the Ugly"? It mirrors the infamous threeway faceoff in that (which was the first time a major film had used 'cuts' to extend a moment of relative inaction, rather than remove it.
Cameos and culture references are there to share something special with the viewer - a nod of recognition and camaraderie between the developer and those in the audience that get the references. You can't really have too many of them, you can only have them be too unnatural, too forced, or too jarring.
Characters turning up where appropriate to their character and situation can't really be overdone, unless you jarringly force the situations for them to appear in. If Nicky suddenly starts turning up in every clothing boutique in games that have no thematic similarities at all, well, that could be jarring indeed, and would be 'too much'.
But if a game needs a security company where the owner is ex-military in Jensen's home town, well it may be equally 'too much' to suddenly expect us to believe there are dozens of such companies all thriving.
The context is more important than how many times/games are involved.