That iOS 4.3 and a new iPad 2, if it then were to happen, would happen at the same time was expected, but what not everybody (non beta users) would potentially not have expected is how it landed.
The all new development IDE
With the iOS 4.3 SDK, Apple officially pushed XCode 4 onto the big stage, pushing back XCoode 3.2.x one which was used as the XCode version for the iOS SDK on any previous build.
XCode 4, which has been available as public preview and beta for many months now, adds a few very usefull features for productivity enhancements, if you happen to develop native applications with Object C and C++, as the integrated interface builder, the much better integrated SCM support and what Apple likely would call a simpler, cleaner, more productive interface and out of my view as user of Visual Studio who never understood how Apple can still be stuck in developers stoneage: XCode 4 finally does realtime code checking that goes through the real compile process behind the scene basically instead of good guessing by an artificial checking which had a tendency to end on code that seemed right until the compiler or linker touched it.
As usually with Apple, this all new great world that we have entered comes at the price of basically relearning all we knew, because XCode 4 really deserves its new major number, nearly nothing is where it used to be, some things are not even available anymore.
Along XCode 4, iOS 4.3 officially favors now the LLVM 2 based GCC instead of GCC 4.2 which was previously the standard one.
I would recommend anyone who has no good reason against this compiler to use it, your compile time and performance will thank you for doing so!
Dropping out the the "old devices"
The second big thing about future that landed is that iOS 4.3 unlike many know from its presentation, not only supports the today released iPad2. In addition, iOS 4.3 also removed support for any of the ARMV6 based devices (iPhone 2G, iPhone 3G, iPod Touch 1st and 2nd Generation), which for Apple likely is a first timer, that they did a major hardware cutoff on a software / OS midway the same major version. We have seen feature limitations already along iOS 4, so the shock is not that large but the impact is still not to underestimate as the consequences on ARMV6 supporting builds done with the 4.3 SDK are not known yet, there are reports of strange performance problems with iOS 4.3 SDK based builds and alike though.
For end users that are on the 3rd generation or newer this naturally is great news, not only because there are a host of new nice features, but it also means that the start to focus stronger on ARMV8 devices happens ealier than the expected iOS5, which will benefit 2/3+ of all currently still in use iOS devices, resulting in either better battery runtime or smoother experiences performance wise.
This is all an interesting development out of my view for us developers that work for or against iOS to achieve their target, as we can work productively now and soon without having to fight the very slow, OpenGL ES 1.1 only, low RAM devices that pestered us long enough if you ask me.