I just put a 6 TB WD Green drive in an A1470 Time Capsule. Wow, was this tricky though - much harder than any of the iMac drive replacements that I have done.
First, I broke two of the small cable connectors while disassembling - luckily it was just for the reset switch and the LED indicator light and these do not appear essential to the working of the time capsule.
Second, initially I couldn't get the captive screws attaching the insides to the top of the case to release. A T8 driver rather than the T10 recommended in this guide eventually worked for me - on my TC these appeared to have T8 heads on them.
Third, the WD Green drive would not sit properly at first. If you look at the Barracuda which comes out, on the circuit board side there are notches in the corner of the drive assembly so that the drive is not full height at the corners. The WD Green drive does not have these notches at the corner and thus would not fit in the rubber mounts at either end of the drive cavity. I had to trim the mounts at the far end of the cavity and the rubber cap at the near end of the cavity using an exacto knife and a pair of scissors to make the drive fit.
Fourth, getting everything back together was extremely tricky especially reconnecting some of the tiny connectors to the motherboard (those that I hadn't busted at least.)
FYI, this was a 3 TB Time Capsule and the drive that came out was a Seagate Barracuda ST3000DM001 which is a 7200 RPM 64 MB cache drive. The WD Green drive I replaced it with is "intellipower" and ~5400 somewhat RPM so I'm hoping it will not generate any more heat than the Barracuda. The Green drive is a desktop drive not a NAS drive such as the WD Red - I would not recommend using a NAS drive in the Time Capsule as most of them have TLER (Time Limted Error Recovery) enabled for use in RAIDs and this is a single drive configuration.
Keeping my fingers crossed... In hindsight this is NOT something I would recommend doing as the risk of bricking the Time Capsule during dissassembly seems high.