I agree with the direction and love were windows 10 is headed, but I hope they stay consistent.
Microsoft has a big tendency to do 180's,Zune,Nokia becoming windows phone, xbox music to grove music, windows 8 and then windows 10, etc....
As for features we will see in the future, I hope there will be a huge focus on Ui elements for the whole Os. I want everything from icons to the device manager updated to match the look we now see in the settings app.(retaining ease of use and features is a must.)
Here is a list of some other ideas.
Most of these suggestions I would never use but I think would be good. Some may be already possible and I just don't know about it yet. Ignoring 3rd party options here as this is all about the core Os.
Tabs in the file explorer would be nice.
Pressing space bar to view documents that you haven't opened.
Support for changing keybindings on shortcuts.
Multiple desktops that allow you to save different backgrounds and task bar setups.
Support for more file types. .rar .7ts etc....
A full dark theme.
The ability to have a white task bar and menu.
A full color editor like hex and a normal square/round color picker.
Allow me to change the length of the search box or just add it to the start menu.
Support for Cortana in more languages/countries
Give Cortana more voice commands like shutting the pc down.
Fix driver updates by making windows the one stop destination or leave it to the manufactures and don't allow windows to update them.
Color options in the calendar for events.
More feature rich apps(I like the design of modern apps but some lack basic features that were available in older apps)
A Password manager could be nice(I probably wouldn't use it)
A unified mail inbox.......
Title bars need color options,
Support for easy theme switching as seen in some android phones.
Customize-able login background.
Slider for opacity levels in the os.
Options for different types of transparency, glossy or clear.
A slider to change the size of the task-bar
A slider to change the space between icons on the task-bar.
Better support for malware removal and other security threats in windows defender.
I liked windows 8 one drive integration and hope it comes back......... Don't hate me I miss my file placeholders.
More options for brightness settings instead of 25/50/75/100 have it be 0-100%
Continually improvements to battery life
I probably could go on much longer but you get the idea. No shortage of ideas for improvement.
Yes, I can see them dropping the '10' in the future.
I use Windows for work. If my software ran on Linux I would've switched ages ago. Don't get me wrong, I don't hate Windows (using 7 and 8; 7 I like a lot, 8 not so much) I just prefer Linux.
I doubt Windows 10 will be the last one. Nobody knows what the future will bring. There will be a day when they might have to change their driver model or any other critical part of the Windows framework. And I hardly doubt this will be possible without a rebuilt os. So my guess is Windows 10 will be around for a very long time but eventually it will be replaced by another major release just because technology never stands still these days. And I think the speed of technical development will rather accelerate than decelerate.
The topic is meaningless and nonsense to debate, Windows will be Windows will be Windows. It doesn't matter if there is no number anymore (visible for the public) after the word Windows. Of course Windows (the kernel) will always have an intern build number and version.