It depends on what the subscription is for; if the open source app is just a frontend to pay for, download and display some proprietary data, then it definitely seems feasible to have a subscription setup.
If it is just a local-only app, like a game for example; you could make money through subscribing to updates. If any of your customers redistribute your code for free, then other potential customers might use the free version instead. OTOH they might like it is open source, so pay for it or donate, while they would turn away if it were proprietary.
Apps like Krita have a setup where you can download the app for free from the website, you can donate on the website or you can download the exact same app via the various app stores for money. That seems like the best option. People who don't want to pay can get it for free and pay by promoting the software through word of mouth. People who want to use app stores can pay. People who have spare cash can donate.
It has a server side component where user data is synced to the server. I looked at Krita, it seems it is a desktop app, not a mobile app and Krita is majorly donation based[0] where they seem to be barely hanging out. There are users on the Windows store leaving reviews encouraging free download[1]. I wonder how people expecting us to work on apps if they do not support us. I have seen some folks in HN argive that open source work should be done for free, and they must do a job if they want to earn a living. I do not think that's right, people are trying to be more transparent by making software open source, but they also need to earn a living. Not everyone can work on both a job and side projects 7 days a week, they're developers with issues like health problems, family issues.
The server side component sounds like it probably could become a subscription, with the app providing a way to advertise that.
Ideally the Windows store would have a way to let users donate what they want rather than have people commenting links to the free downloads.
I definitely agree that proper funding for open source work is important. There are lots of companies who provide this by having their employees work either full time or part time on open source. There are various other ways to get paid for work on open source, some of them listed on the pages below.
If it is just a local-only app, like a game for example; you could make money through subscribing to updates. If any of your customers redistribute your code for free, then other potential customers might use the free version instead. OTOH they might like it is open source, so pay for it or donate, while they would turn away if it were proprietary.
Apps like Krita have a setup where you can download the app for free from the website, you can donate on the website or you can download the exact same app via the various app stores for money. That seems like the best option. People who don't want to pay can get it for free and pay by promoting the software through word of mouth. People who want to use app stores can pay. People who have spare cash can donate.
https://krita.org/