While I guess this may affect Mono due to direct competition, will it have any direct effect on Xamarin, whether adverse or positive?
I think it will help to improve the Xamarin eco-system but will make Mono less or irrelevant in the long run.
I don't think it will effect Xamarin APIs and services so much. You need them if you want to debug C# code on iOS or Android. You may also need there APIs for app development as it would save you a lot of time even if Xamarin started using .NET Core for there runtime (which would probably be good if Mono and .NET core merge).
Only issue iv'e ever had with Xamarin is there licence on the Mono runtime doesn't let people use it on iOS and Android ect without a licence if they don't need the Xamarin APIs... for indie game devs this can be an issue. .NET Core will fix artificial limitation with its licence and give people more reason to use .NET in general (takes away the fear)... in the long run that helps Xamarin as future projects people do may require there APIs if they want to be productive.
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