Yes, it is a shame. But: I will add it, along with Windows support.
Indeed, I'll go further. I'm really starting to believe that the only way not to get royally screwed as an app developer is by abandoning the "major" platforms -- which all want to turn you into a serf -- and target OSS platforms like Linux. I'm honestly tiring of dealing with the artificial roadblocks Apple (and Microsoft is no better) throw at me to further their own ends. I actually analysed SteamOS with this intent, but sadly it looks like SteamOS is geared towards the "living room" experience.
Anyway, long story short: there will be Linux support in 2018.
zenAud.io is designed for live use, so it currently doesn't have a piano roll -- instead, you define record loops using editing tools in the arrangement view and record MIDI or audio into it. You can also drag and drop to import standard MIDI files into the arrangement if you want to use pre-written stuff.
I realize this is a big limitation, but we intend to add a piano roll in the next few months.
https://zenaud.io
Send me an email at mpercossi at zenaud.io , always fun to talk to fellow audio devs :)
And for all the vim lovers out there -- my app supports vi commands for movement and editing :)