I thought also that desktop development and PCs are dying. Until I saw a person working with Google Sheet on a 10" tablet in a rural area that only have GPRS/Edge connection, then I am sure that PCs and desktop development won't die that soon 
Actually, mobile market has
already displaced desktop and in that sense, desktop development / PCs are becoming niche market. But in my opinion,
mobile may not be necessarily limited to
tablet or
phone.
For instance, I have here sitting on my bench
Raspberry PI 2 in box and
Utilite Pro that already provide desktop-like experience with display/keyboard/mouse connected, while running desktop-like OS. Each of them is more powerful than a desktop PC that I had several years ago, while using only a couple of watts, if not less. I still keep the vision that eventually mobile/embedded devices will become a desktop PC replacement, where you just "dock" your smartphone and it becomes a desktop-like PC (and they are already working on
something like that).
I think supporting mobile platforms in Delphi was a really smart move and IMHO actually the only thing that kept Delphi alive. I see no point in VCL, specifically because it is limited to Windows; in that sense, LCL has proven to be much more flexible - being very compatible with VCL yet being cross-platform.
Also, I don't share view with other people who think that Windows is and will remain predominant - at least every relative I know (and my wife has eleven brothers, some with grandchildren, so make your math) and people from professional/scientific area that I work with, were quite unhappy with Windows 8 and don't like Windows 10 either; moving to different platforms, including Android tablets, iPads, Macs and/or Linux has been predominant lately. I myself, a long die-hard Windows user for over 25 years (since Windows 3), who never particularly liked Linux, have finally switched to it and am not going back. So no, I'm not that optimistic about Windows, and as some suggested to support this platform in Delphi exclusively, throwing away cross-platform, would essentially mean complete death for the product, even in absolutely unrealistic scenario where it would become open-source/free.