I know rapid start magnetic ballasts for F32T8 lamps exist. I own one. What about magnetic RS ballasts for four foot T5 tubes?

Based on what I have heard. T5 are used only with electronic ballast(except older low wattages models. 13W and under). correct me if Im wrong.

Higher wattage T5 came quite recently, when not too expensive electronic ballasts already existed.
I had a look into lamp's electrical parameters (Osram) and it look's like:
Lower wattage T5HE (21W and below) are 0.16A lamps, so might operate on the generic "low wattage fluorescent" preheat magnetic ballast, but only on 230V (the F28 and F35T5HE are 0.16A too, but have too high arc voltage even for 230V mains). The F1T5HE would be slightly underdriven.

F39T5 might operate on F36T8 (EU) or F32T8(US) ballast, but i guess only preheat, as these lamps would have too high ignition voltage for RS.

The non miniature T5 lamps of 14W and higher are based on a krypton buffer gas. Rapid start magnetic ballast and all of the electronic ballasts that emulate their ignition behaviors (The american Rapid Start electronic ballasts) can't ignite any type of krypton buffer based fluorescent lamps. Nor T5 HO and HE, Nor T8 in 18W,36,58W and 70W and even nor the T12 of 100W which is also krypton buffer based. This is because krypton and also argon-kypton mixtures have both too high ignition voltage for rapid start ignition mothed (The mothed of the magnetic ballast ones) then pure argon.

I've personally never seen a rapid start F28T5 ballast. I believe they most use 'programmed start' electronic (rather than T8's where you usually see Instant Start)
 
I know for a fact that a F32T8 Instant Start ballast will light a F28T5 lamp (but ofcourse it will overdrive the lamp some, nor do i know how safe it would be once the lamp reaches EOL)

Eventually i want to get a 2xF28T5 fixture (or even just ballast) once i see a good price LOL just to check it out. And i'd love to get ahold of one of the the new VHO T5 fixtures

The non miniature T5 lamps of 14W and higher are based on a krypton buffer gas. Rapid start magnetic ballast and all of the electronic ballasts that emulate their ignition behaviors (The american Rapid Start electronic ballasts) can't ignite any type of krypton buffer based fluorescent lamps. Nor T5 HO and HE, Nor T8 in 18W,36,58W and 70W and even nor the T12 of 100W which is also krypton buffer based. This is because krypton and also argon-kypton mixtures have both too high ignition voltage for rapid start ignition mothed (The mothed of the magnetic ballast ones) then pure argon.

Proper rapid starting applies such voltage such that lamps do not strike with cold cathodes as well as cathode voltage.  The lamp strikes as cathode warms up and lamps should not start faster than the ANSI recommendation (I think 500mS or so).  

For a 2lamp F40T12, the OCV range is 256-330v. Because of the OCV to lamp matching, the ballasts are specific to lamp type.  

Electronic rapid start ballasts that once existed could not hold the OCV within range and often had enough to cold start the lamp if you were to start with one lead missing from each end.  When properly wired, they often started lamps faster than recommended by ANSI.

As such, NEMA publication shows electronic RS to improve life in longer running application (but efficacy is reduced) and offered no advantage over instant start in shorter cycles.  

Program rapid start keeps the OCV as low as possible upon power-up, then provide cathodes heating then apply a high OCV providing a superior starting characteristics than magnetic RS.  

NEMA data:


You can find a handful of electronic rapid start ballasts, for low-cost CFL units and legacy F40T12 replacement ballasts. Programmed rapid start is superior in every way, so "rapid start electronic" is quite rare.

It's probably possible to do it with magnetic if it used a time delay circuit inside with the cathode heater power coming on right away, then the delay circuit powering up the very high OCV main arc source.