If anybody still has concerns about this, I've successfully tested stock JellyBean and KitKat varients of Samasung's stock TouchWiz ROM working on the Qualcomm release of the Galaxy S4 (GT-i9505, aka S4 International / JFLTEXXX), plus CyanogenMod 12.1 and now the Marshmallow Cyanogenmod 13 nightly releases... all except one of the early March releases have been absolutely fine (after I've applied Martin Gerczuk's rSAP Installer).
As mentioned above - one set of the CM13 Nightlies (around 03-MAR-2016) failed ont he rSAP installer - indentified as incompatible hardware.
I've had a couple of the nightly builds (around Jan 2016) where I've noticed REALLY pronounced battery drain while Bluetooth is running - I need to setup some Tasker actions (if battery drain detected: shutdown Bluetooth), but the last few builds have been fine.
On more recent Nightlies, the phone is now identified as "JGEDLTEUE" instead of "JFLTEXXX", but still installs perfectly.
Car: Audi A6 TFSI @ 375bhp, MY12, MMI touch, BT High.
Primary: LG G5 H850 stock MM6.0.1.
Projects: SGS2(GT-i9100 on CM13) + lots of Nexus7's with various builds.
eBay soon: SGS5 Prime (SM-906K), SGS4 (GTi9505), SGS4 Active (GT-i9525).