If you create applications for iOS 6 (iPhone 4), how compatible will they be with modern versions? And vice versa - what is missing in the old Target?

Question

iOS

The question is in the title.
Why such a question - for a long time there has been an idea to create a pirated "emulator" for those who have Windows, but who want to develop for OS X and iOS.
I myself use VPS, but there are certain limitations, and it still costs money.
The "emulator" will be a pirated image of OS X running in VirtualBox or VMWare, of course modified for ease of use, like Genymotion, it is also based on the VirtualBox SDK.
With reverse engineering, everything is perfect, if necessary - I can disassemble the entire OS X with Xcode and iOS Simulator and the entire VirtualBox, make x86 from x86-64 modules, take the old version of the OS and "merge" with the components of the new one, modify VirtualBox much better than its creators, so all this will work even on AMD without AMD-v and with 2 GB of RAM, etc.
But time!
Therefore, at first, it is necessary to limit ourselves to what can be achieved quickly enough and to be as “unpretentious” as possible to the power of the host, so that it does not require Intel VT-x, but also works with AMD-v, or better without hardware virtualization at all, in order to run on VPS with Windows Server.
And this is offhand OS X 10.6 (it can even be 32-bit), you can’t count on more.
And, therefore, Xcode 4.3-4.6, corresponding to the era of iOS 6 and iPhone 4.

Answer 1

Nobody supports iOS6, very few people support iOS8.
The idea is pointless.
1) Most likely swift will not take off (not sure)
2) All the goodies added after iOS6 will not work.
There will be no sense from such a simulator