They will be either on Android or iOS or Windows devices always and getting your course adapted among these devices is of primary concern.
I definitely agree courses need to be designed first and foremost for iOS, Android etc. But I personally look forward to the day when courses are designed with FOSS mobile OSs in mind (also true to the spirit of Adapt being FOSS under the GNU public licence. I believe/hope this is coming soon, especially with the advent of the much-anticipated Librem5 phone by Purism.
Learning and quality learning design needs to be free and open to all, and the Adapt developers have made a great contribution!