Assault Marines as Troop choices:
Whilst Tactical Squads are great (and quite overlooked IMO), I think Assault Marines really should be a Troop choice. According to the fluff, marines join assault squads before tactical squads so to me this makes sense. There are also a plethora of good options in Fast Attack that are fighting for space (Vanguards, Storm Talons etc). At the very least it would be great to see it as a chapter tactic even if it meant bumping Devastators into an Elite slot or some other type of Force Organisation tax.
Apothecaries as a stand alone option:
Command squads aren't really worth it in the current codex, you're much better sticking a captain in with some terminators. As such, apothecaries don't get much table time despite being pretty awesome. Codex : Blood Angels fixed this with their Sanguinary Priests and I'd like to see this as an option. Same with Chaplains, have a toned down Chaplain would be cool.
Not a job specialist as such because I think they are covered well enough but a Chaplain/Librarian Dreadnaught. This is probably not going to happen because FW have a Chaplain Dreadnaught model but this is a wish list so...
You need something to deal with enemy fliers. The Talon is okay but a bit vulnerable in a duel and the Raven is quite expensive. At the very least have a flak missile upgrade for tactical squads and or hunter-killer missiles. An upgrade for the whirlwind would do this easily enough.
Special Weapon in a combat squad:
I appreciate having a heavy weapon in a 5 man squad isn't really fair but a flamer is. Being able to give a tactical squad of 5 a special weapon would make a Razorback a viable option to build around.
All the new armies have a big shiny toy, be it a walker or flyer and I hope this codex is no exception. In this regard, I don't really know what I'd like to see. I don't think a flyer is necessary as they've already got two. A walker also seems a bit redundant as there are already dreadnoughts which can go toe-to-toe with most walkers already. An all-out offensive heavy-tank would be cool, a Land Raider size beast with no transport but a massive cannon/Gatling gun.
Kits with all the options:
It annoys me that, for instance, an assault marine sergeant can take a thunderhammer but one isn't included in the kit and they aren't particularly easy to come by. This annoys me mightily and is something I want to see fixed.
New Character models:
At the very least there needs to be a new terminator captain, the old model just doesn't cut it anymore as far as I'm concerned.
Would be awesome. People rarely take 5 or 10 of these. 7 seems to be the magic number. Having a duel kit means you can get those extra two models for each squad without having spares knocking about.
This is a long list but I think they are viable considerations and I'd be happy if only one or two are done. As an aside, I hope that the codex isn't too heavy on Ultramarines. This might seem odd because this blog is focused on Ultramarines but its largely because I'd rather they got their own supplement. This might help steer newbies away from doing the big U as the default army, especially as the starter kit now focuses on DA.
I'd be really interested in hearing what you guys want/don't want to see in the comments below