Her cant-kill-me barrier looks as she can project it only around herself, with no mentions of contrary encountered anywhere i looked (Wizards of the Coast, Lucas Arts etc) i presume her to be unable to shield others - sources telling otherwise shall be welcome - thus making her ult self-cast only and adding 10-20 to her base ad to compensate seems reasonable enough to do so.

She can cast it on any ally within range.

He's suggesting a tweak to Kayle. I'm going to assume you're been reading other topics on Kayle, and caught my comments that Intervention being able to shield allies has lead to Kayle being quite team-dependent.
However, 10-20 base attack damage does not make up for changing Intervention so drastically. Back when Intervention was self-only, it was a flat 4 seconds with a cooldown of 60/50/40/30/20. It was also her E ability; Righteous Fury was her ultimate (I forget the exact specifics, but it had a much longer duration back then). Kayle got nerfed a lot when they made Intervention able to target allies because they nerfed all her other skills to make up for it (Riot has admitted that back then, Kayle was a "lopsided" champion). Your "tweak" would just drive Kayle down into the depths of "never heard from again."

I just got killed the other day by Karthus' Q while my ult was on. I'm really tired of it being a semi immunity. That would be the only thing about her I don't like. I still like her ult, but it's so situational and barely useful at all if one of these non immune abilities happens to be used in the game she's in.

Just fix Kayle's Ult, that's all I ask. It's only a 2 second duration immunity, for an ULT. Make it an immunity against everything in that time period for the love of all that is holy....

20 ad...really, even though shes more carry orientated she will forver be a support/mediorce dps till her E becomes either a toggle or a passive ability. if she cant do her usual support role then why on earth would anyone take her when trynd can do the same thing but 10x better and his ult last twice as long. for kayles ult to be self cast it would have to 5-6 seconds to match.

Lol her ult isn't op stupid. Look in dota and hon same-ult concept = global ult.