I think you have a big logic flaw here, there´s no such thing as X-Coins, XMR itself has nothing todo with those x11 coins you prolly mean.

XMR as a currency symbol is simply used because its the ISO standard: http://de.wikipedia.org/wiki/ISO_4217
All currencies who aren´t bound to a single country or area are starting with X, like XBT is the currency code for Bitcoin and XCP is the code for Counterparty which have all totally different codebases.
For example MRO as a currency code was already taken by the Mauritanian ouguiya, the national currency of Mauritania.