There has been for some time an idea that eventually Christianity and Islam would put aside their differences and merge into one super-religion, pulling up aspects of each and perhaps dominating the Earth. It has been suggested, even, that the somewhat more polytheistically inclined Hinduism could absorb both, and what the heck, throw Judaism and Mormonism and Sikhism into the mix, thus creating for the first time in recorded history a single religion commanding the fealty of a majority of the world's population. The idea is given to several different authors, who have taken different angles -- Arthur C. Clarke for example writes in his 1992 The Hammer of God (not to be confused with the Led Zeppelin biography Hammer of the Gods) of a not-so-far-future fictional Earth where "The sudden rise of Chrislam had been traumatic equally to Rome and Mecca...." growing swiftly to a hundred million adherents, abetted by cultural and economic difficulties squeezing the parent faiths.
But as a matter of practical experience, consolidation is an unlikely path for any major faith; each is more likely to split into multiple smaller sects, and any reconciliation between sects of different faiths will tend to be far outside the mainstream of beliefs falling under the umbrella of the faith. And so, even as there are conciliatory voices today who would claim that all these different faiths are simply different paths to the same Creator, (indeed a position held, if somewhat more obliquely and indirectly by Pandeism), the greater tendency amongst the faithful is to ramp up greater indictment against beliefs discordant to their own. Even if, it turns out, those faiths fall under the broader ends of the umbrella of their own religion.
There is in fact, by the way, a faith group operating under the name 'Chrislam' and purporting to carry out the idea discussed here, attempting to meld assertedly reconcilable elements of Christianity and Islam. Or, actually, there are two groups. Both are in Nigeria. Oh, they started out as one, but had a schism somewhere along the way and are now, if not bitter enemies, passing acquaintances who don't pass up an opportunity to snipe at one another's divergent doctrines. Ironically, if unsurprisingly, this is what Arthur C. Clarke forecast for his fictional version as well. This, before a later inevitable eventual turn to a world where the only divide was between proponents of Atheism and Deism (presumptively including Pandeism).
Naturally, we might abbreviate this to Xlam (or perhaps Xslam?) by using the conventional substitution of the 'X' for Christ. People typically imagine that this arose with the intention of insulting Christians, but really the origin of the X as a substitute for Christ in Xtian, Xtianity, and, naturally, Xmas, is something of a mystery -- it might indeed have been intended by non-Christians in a derogatory sense, but it just might, as well, have been a Christian connivance. One perhaps intended simply to abbreviate, or perhaps complexly to obfuscate. The X is after all something like a leaned-over t in its resemblance to that most deathly of reminders, the cross. In some fonts (and in the multiplication sign) the lines are in fact perpendicular. And, even more interestingly, in ancient times, Jesus Christ was sometimes abbreviated by Christians familiar with the Greek alphabet with a symbol combining the letters "Chi" and "Rho" -- roughly represented in the Latin alphabet by X and P, respectively. It is very easy to see how those earnestly and noninsultingly referencing Jesus might have whittled their representation down to the point where X marks the spot.
But then again, if X means Christ, doesn't that mean our X chromosome is the Christ chromosome, the X-Acto knife is the Christ-Acto knife, and the Uncanny X-men are really the Uncanny Christ-men?
"Signs of Xmas" in Changing Signs of Truth: A Christian Introduction to the Semiotics of Communication, by Crystal L. Downing, pages 89-90.