I know sometime it's available a sort of virtual ILS in instrument view...
I think it could be useful to be able to create a custom ILS.
I mean: registering a point as touch down position, setting up a glide slope and course.

What do you think?

You can do this already by adding your own custom airfield. This is achieved using the Data Creator on SkyDemon Plan (for PC). You can then save your custom data to the cloud and open it on your mobile device(s). You just need to create a runway with the thresholds at whatever coordinates you choose. Hope this helps!

Can you set up the glide slope also?

The pseudo ILS functionality will be available if your runway has full threshold coordinates specified and elevation. Glide slope will be enabled if you have enabled it in your SkyDemon settings. You define the angle there too.