It was put out awhile back in semi official form that we were not getting anything past 4.1.2. I haven't kept up but it appears the i9100 is still on 4.1.2 and even if it got 4.2.2 it was still be HIGHLY doubtful not only 4.2.2 wouldn't be developed for our varient but that Sprint would choose to spend the resources on testing. On some occasions a old variant update is moved to carrier testing and the carrier rejects testing outright.
4.2 on AOSP is the last you currently get to see of WiMax. There are no WiMax phones with android updates in development.
As far as AOSP projects and roms go 4.3 is available sans WiMax and while the CM builds seem a bit rough (Mic volume is very very very low on speakerphone) the 4.4 CyanogenMod 11 build Dastin has is working great. I haven't had GPS working this will since 2.3. Its smooth and fast but 4.4 AOSP is the end of the road for this phone to be honest. Its out of system space so it gets hairy from here on out. Custom rom users will have to either put up with stripping out apps or attempt to re partition the device for more space.
Also Samsung and Samsung support will almost never know when a phone on a US carrier is pushing an update, especially a Sprint phone. US carriers do alot of testing with all of their customization's. Samsung pushes a build to Sprint and days to weeks later it might get green lit. Samsung obviously knows when a phone is still being developed for and has a time frame for international device releases. However tech support almost never has a schedule that is not already posted on every android site in existance.
Current Phone Nexus 5 | Black 311 | CyanogenMod 11 | T-Mobile
Old Phone Galaxy SII Epic 4G Touch | CyanogenMod 11 | FI25 Modem
Desktop i5 2500K @ 4.5Ghz | ASUS P8Z68-V PRO | 16GB Corsair Vengeance 1600 | Seasonic X750
MSI GTX570 TF III @ 950/1900/2300 | 2TB 5900 + 2X320GB 7200 RAID0 | Zalman CNPS9900 MAX