I'll probably end up doing it myself or (more likely) just living with the changes SM gives, but I have a suggestion/request for an invisibility overhaul. Everyone always [censored]es and moans about chameleon being to powerful, but it's really fairly worthless until you assemble the 100% chameleon set, which is when all the [censored]ing is appropriate, and it breaks the game/makes it boring. Because of both those reasons I never touch Chameleon stuff (plus the invisible shader constantly is annoying). Invisibility however is much more useful/overpowered, but doesn't get any attention for balancing for some reason. The drawbacks (activating stuff breaks it, or attacking) are incredibly easy to avoid entirely (activating things to break it is essentially not even a drawback, all you have to do is time when you activate stuff before you finish the animation for refreshing invisibility) or partially (hit and run tactics for attacking). I've always recognized it as a problem (Morrowind) but love it to much for traveling without being harassed (and the previous reasons, to a lesser extent, as well) to give any possible solutions some thought.
However, when I started my new character and picked the thief birthsign (from BE) I immediately fell in love with the design of 'Slip Away'. The small duration made its use tactical, I couldn't use it to just wander through a cave or house with much higher level guards without pause, but instead I had to sprint from dark area or corner to corner, and pray that I wasn't detected while I was exposed; and the huge fatigue cost/silence prevented it from being spammed. Until I had enough money to by the lowest level Invisibility spell, and fell back into my old habits (IE not using slip away). I use Audacious Magery (basically Fizzle, but with more penalties/chance of bad things happening, which I find amusing), so the small balance provided by SM only making invisibility (or maybe its vanilla? Haven't played vanilla in so long...

) available starting at Journeyman didn't really mean much, other then possibly damaging my stats/getting disease etc. from Audacious Magery when I cast it, which is easy enough to fix and generally not an immediate problem.
And I just lost my train of thought and this is getting long, so here are some suggestions I'm throwing out as possible balance solutions, one or all could be applicable if you want to make it really hardcoe :shocking:.
What I think are necessary regardless of optional penalties-Journeyman and higher availability only.
-Incredibly short durations, ~5 seconds from the cheapest version, that increase with skill (IE Master level version lasts longer)
-Penalties scale inversely with skill (IE Master's have the fewest/least severe penalties)
-Remove the ability to create invisibility spells
And then some suggestions as possible penalties.-Silenced for duration and longer, depending on skill
-Stunted for duration and longer, depending on skill
-Steady Magicka or Fatigue damage for duration (to simulate the stress of maintaining the spell)
-High Magicka costs
-High Fatigue costs (IE how 'Slip Away' works, takes a chunk of you're fatigue)
-A Health cost (going invisible is bad for your organs... or something, I don't know)
An idea, thought by no means thought out completely as far as balance/fun is concerned, for how it could scale
Journeyman: 5 second duration, silenced for 10, stunted for 10, costs half your fatigue, higher magicka cost
Expert: 10 second duration, silenced for 10, stunted for 10, costs a third of your fatigue, higher magicka cost
Master: 20 second duration, stunted for 20, costs a fifth of your fatigue, higher magicka cost
Or if you were feeling particularly ambitious, tie the penalties to your skill perk level, so a master could cast a short duration (Journeyman) spell but only get stunted for 5 seconds and have it cost a fifth of his fatigue (as in this example).
And then possibly a Master level spell for traveling, maybe a minute duration or two minutes, but breaks everything you own and silences you for most of the duration. This would prevent you from using it for anything other then traveling, and most people use one of the big magic overhauls, and as far as I can remember, all of them have a way to magically repair your equipment that someone capable of master level spells would more then likely have. Otherwise it gives more use to armorer!
And I had an epiphany, a completely different way of possibly doing it that may or may not be even more fun/rewarding/challenging. Leave the way the spells are, and simply make them cost a filled soul gem. Gives a use to soul gems which I thought were completely useless in Oblivion (enchanting is terrible, so you almost always end up vendoring them).
Anyway that's my proposition for possible ways to balance invisibility, that post got much longer then I planned, but I figured I'd ask you rather then make a thread about it first, since I love all the mods you do, and BE gave me the idea's for balancing it.