GBAS is quite new, and won't be able to replace ILS as a standard for quite some time. One reason of course is that it is only certified for CAT I operation and although CAT III trials are promising the introduction of CAT III GBAS/GLS is not anywhere close.
However a GBAS ground installation is quite a bit cheaper than ILS installations for all supported runway landing directions, so there is a certain incentive if the decision is to either install several ILSs or one GBAS installation.
Nevertheless, a GLS compatible multimode receiver is standard equipment on newer boeings and airbusses, our 737s since 2006 have it equipped and my outfit has been certified for operational use of CAT I GLS approaches since 2009 on the 737 fleet. Autoland/rollout is not currently certified but has been demonstrated and shows better performance than on an ILS especially since there is no need for any protected areas around the runway. Sadly there is only one fully certified GBAS airport in our route network which we do not use very often (EDDW) and another with a test installation that can only be used on the PM side currently (LEMG). There are plans to introduce GLS in EDDF and EDDM during the next few years, but so far there is no introduction date.
Although the 737NG is equipped with dual FMCs the whole GLS operation is based on the MMR and does not require the FMC to be setup for an GLS approach, the MMR receives both GPS and VHF datalink signals and produces an output for the autoflight system and instrument presentation that is identical to an ILS signal.