i'd say you'd be pushing it trying to get all this in an ion. i use my ion with a caribou mf, and that takes about half the pack (or a bit less if you compress it a lot - which i don't like to do). the MLD shelter and bug net will take more room, and a prolite 3 (and perhaps z-pad section) is another fairly big chunk. then water filter, stove and canister, etc. are a few more solid items. then fitting in a rolled up precip is another chunk of space. and then the unknown is food. i'd say, as a guess, it won't all fit, even with only a weekend of food.
the ion takes a fair amount of gear, but usually something has to give. i did a three day no-cook hike (down to 30 degrees) out of it in november and everything fit, but just barely. check a thread about it at:
i had to tie my insulation layer around my waist until i ate some of the food down, and when i had to carry max water (3L) for a long dry stretch, it was good that i had cleared out most of the food space. i used a caribou MF, MLD bivy, GG Nightlite 1/4" cut down pad, no cook, etc. and i had my camera/ipod in a case on the strap, and a 20oz water bottle on the other strap, AR-style.
it's a GREAT pack, but you definitely have to go pretty minimal, in fair weather, to pull it off.
to pare your list, you might:
1. Replace Prolite 3 with GG nightlight THIN pad, rolled up and everything packed inside it in the Ion.
2. Use Aquamira instead of filter, and repack into small droppers.
3. Use a simple alcohol stove and a few oz. of fuel.
4. If you need rain protection, consider MLD Poncho/Tarp - replaces shelter and precip, and gives you a packcover. if bugs are mellow, you could just use a headnet while sleeping or whatever. if they are bad, you need a place to hide though!
5. If water is abundant, just use a 20oz bottle AR-style on the strap. Since the Ion is usually pretty full for me, trying to deal with a hydration pack (filling, packing it in) seems like it would be a drag. If I need to carry more, I bring a 1L or 2.4L Platy tucked into the pack and just use it to refill my 20oz bottle as necessary. I'm not a huge fan of hydration systems, YMMV.
I've been considering the MLD gear Arc pack (in the more durable black) as a small and light pack that has a bit more space with external pockets and all that. I'm a big fan of Aquafina bottles in side pockets for water carrying.
Just a few ideas!