Right now, as far as the GT-I9500 - UNKNOWN. Right now, to my knowledge, no maintainers have it, and none I have talked to are particularly interested in it.
Does this mean that no one, ever, will touch it? No. Someone might pick it up.
But it's pretty much: GS4s with Qualcomm chips and unlocked bootloader = highly likely (in fact, as Steve has shown, pre-alphas exist).
GS4s with Exynos5 "Octa" - Indeterminate. Far less likely - not impossible, but not highly likely either.
Kraits are getting to be REALLY easy to support... If you want a device that is likely to get good CM support - get something with a Krait and an officially unlocked or unlockable bootloader. Or even better - don't buy a device based on what it could be, but what it is. If CM is critical to you, buy a device that is already well supported.
I don't know of anyone who has an I9505 either, however it's so similar to the T-Mo variant that it shouldn't be too hard for someone to pick it up.