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We've seen the iPhone OS influence parts of OS X from the start, and it makes sense, if Apple have OS X on laptops, and 'OS X' on a phone, then the phone is going to have the least battery life. If you create something for the phone that is efficient and can be ported to the 'main' OS, then laptops (and desktops) will enjoy that drop in computation/power use too.
I can see them merging in the future, I'm not sure what it will look like, but I can imagine Apple will be clever.

As to the change from Objective-C. I've had a look at Objective-C and I'm not 100% on it.
Syntacticly it's very different from C and Java, even some of the scripting languages such as Bash and Perl. I understand Objective-C is based (syntacticly) on Small Talk, and that's where it inherited it's objectiveness.
If Apple more to another language, I'd hope that it was one that conformed syntacticly more to the C like syntax, but I could see this being a problem for current applications. Indeed, I believe Objective-C 2.0 brought the "dot syntax" to help developers get used to the language, but the books I have read seem to dissuade one from using it as other programmers tend not to use it...

From a more user standpoint, I can imagine a time when Mac OSX gets an application layer similar to Front Row or Dashboard. We may even see Macs being able to run iOS apps.

One thing that is happening is that apps on the Mac are heading towards being single window entities. Most of Apple’s apps do this, and a lot of other apps are heading that way. There is less need for floating palettes of options, and iOS shows how this can be managed quite effectively. The iPad shows that you can do this on a bigger screen, and with a touch interface which is less demanding than a mouse.

Like .Net Compact Framework that Windows Mobile has had for years now (mobile apps will run on a desktop fine)

Nah it'll never take off

It is possible, but it's ignoring one central point - Mac OS apps are WIMP driven, iOS apps are touch driven. Those are not the same thing. Plus I doubt the Mac OS market would go for an app store model at this point. Undoubtedly over time the 'back end' aspects of the OSs will merge - essentially there's no reason why a lot of the frameworks shouldn't be the same, especially once phones get multicore processors - but I can't seem them ever being 'merged' in so far as you having to install iOS on your desktop. Unless or until all Mac desktops have some sort of touchscreen interface anyway.

I think an iMac Touch would be hard to use from a purely physical stand point. Where do you put it? Would it be a screen like it is now, a drawing board? Something else? I'm not sure that either of those would work with a touch interface - it would be too tiring. The iPad works because of it's size - make it bigger and you start to create an unwieldy item.

Moving from a WIMP to a single screen for applications would not be too hard. As I said, a lot of Mac applications are si gle window devices, and the iPad does show how you can work in such an environment. For the Pro users, I can't see the WIMP being dropped, but for the more casual user, and iPad type interface could do the job. It would also have the benefit of hiding the filing system from the user, reducing confusion and making sure that things are put where they are.

I think Apple could make the Mac OS the first big OS that does something like this. Especially in the whole hiding the file system type thing.

In the old classic Mac system there was a thing called Simple Finder. On System 7 I think it literally simplified everything to massive buttons, and on later versions simplified the menus and limited what you could do to break the computer.

So, I can see how iOS and OS X could be merged so that the iOS form is the simplified, easier-to-use system, perhaps incorporating touch screen technology. That would leave the full-on OS X UI for those who need to work with it.

When the iPhone came out, I thought that the OS could be scaled up. The iPAd shows that this is possible. Scaling it to a simple Mac interface would be a great idea. Steve Jobs said that the iPod Touch was “training wheels” for the iPhone. I see the logic - if most people who use an Apple product are iPhone users, then why not use that knowledge and get people using Macs too?

I pity the poor software developers who will have to rework their applications yet again to fit in with a new Apple scheme.

I would have thought that the features that were needed in OS X would be adopted into the OS from iOS4 as needed. First might be touch screen once they mac touch screen variants of the laptop or desktop range.