What are the chances there will ever be an untethered jailbreak for the iPad1 A4 in the future? 4.3.5 untethered ever?
Some folks like to say never, but as others say, you should never say never...
Apple patched the exploit used by ion1c to untether the 4.x jailbreaks in 4.3.4 and it is a lot of hard work and effort to discover a way to untether a jailbreak.
With IOS 5.0 just around the corner the question is why would a talented jailbreak developer waste any of their time searching for, and assuming they find one, then exploit a bug to make an untether for 4.3.4 and 4.3.5, which are already more of less obsolete?
Doing this stuff is not trivial. It takes many weeks / months of hard slog. That is why most folks say it will never happen. Nobody who has the skill to develop it is motivated to do it. They are spending their time finding exploits for IOS5 (and as we know from recent news they have 5 userland exploits already in their bag)!
If you want to be a little more optimistic, one of the userland bugs discovered for IOS5 may actually one day allow the 4.x versions to be untethered too. But there is no way that will be released until a 5.x jailbreak is well and truly out. Then and only then you might see an untether for them, but that is a really long shot and by the time it comes out you will probably rather want to be on the 5.x jailbreak it is associated with...
Also will iCloud force me to upgrade with every new iOS version?
There is a fairly good chance IMHO that once you are committed to iCloud you will have to keep up with the major IOS5 updates to some degree, but it is highly unlikely Apple will force you to take every singe minor IOS point upgrade in order to keep using the service. That just is not practical. You can't stop folks from using their device just because they are not in a position (for whatever reason) to do a minor point update, whether it's OTA or via iTunes. It would also be a logistical nightmare for both them and us to manage, particularly in a corporate environment.
It is more likely to be a little more flexible and tied to major point releases. e.g. 5.x. for certain features so that their millions of users are not disadvantaged.