A Stack Exchange employee just said the following regarding the mobile site:
We are actively working on the responsive design that works on both desktop and mobile, based on screen size. Once that is finished and perfected, mobile web will be slated for complete removal.
I was recently visiting relatives in India. Most of the time, I could access Stack Exchange through a fast Internet connection and could easily do things on the site using the responsive site, on my modern mobile device. However, there were times when I'd have to access the network through an extremely slow connection, as slow as dial-up.
Basically, mobile data providers in India offer "unlimited" data, and limit daily usage to between 1-1.5 GB per day. Beyond that, your speeds are reduced to much, much slower speeds (in my case, 64 kbps, which is just a tad faster than dial-up). You might think, you're not likely to use so much data in a day, as you can use Wi-Fi, right? Unfortunately, my relatives and (mostly) everyone living in the suburbs have disconnected their home broadband connections (DSL only) in favor of doing everything over mobile LTE data.
I maxed out my mobile data allowance quite a bit during my trip. While (I'll be honest) I was using the Internet too much sometimes, most of the time it was because I accidentally left some background process running on my laptop (which would be tethered to my phone), partially or fully depleting my allowance early in the day. The responsive site simply would not load over the slowed Internet connection. The mobile site, on the other hand, would load relatively quickly and be almost completely usable on the slow connection. I'd like to be able to access the network even if my connection ends up slowed.
Also, this isn't just an India problem: many less-developed countries have slow home connections with no access to LTE or 3G networks. Even here in the U.S., around 2% of Internet users use dial-up (with one state having a rate of 4%), and I'm assuming a significant (slightly higher) percentage use home broadband connections less than 1M (one of my previous classmates living in a Houston, Texas suburb had a 256k DSL connection, the fastest available in their area). Keeping the mobile site up will tremendously help users on slow connections access the network, due to the sheer overhead of loading external assets on the main site and help keep the network open to a more diverse audience.
Another concern, aside from network speed, is the fact that the mobile site still works over many browsers that are no longer supported and broken on the main site (e.g. Internet Explorer 11 as of November 2019). If one is forced to use an old browser for some reason (e.g. they're on an older work machine), they can still use the network using the mobile site (albeit not in the same way they used to be able to before, but still better than the current desktop site state). I've been vocal about SE maintaining IE11 support before, and under those posts, you'll find comments from many users who complained about this recent omission of support. (A real example: many cities in the Netherlands use Windows 7 with IE10 because their software won't work on later versions of Windows or IE.)
I'm fine with SE not developing new features for the mobile site and only fixing vital bugs for it. But, for the sake of users on slow Internet connections (and, as an aside, for users made to use older browsers), please do not completely remove the mobile site.
A few questions about my connection in India that I expect will be asked in the comments:
It's rather far-fetched that everyone would use the Internet on their computers by tethering their phone. Aren't mobile data wireless routers that provide home Wi-Fi available?
Yes, and some of my relatives do have them. Those provide an expanded limit of around 3-5 GB per day, but since that allowance is shared, it's still easy to max it out since different people are using it at the same time.
What about public Wi-Fi?
Unfortunately, the Indian government requires operators of public Wi-Fi services to collect and verify cell phone numbers of their users. I don't connect to them for privacy reasons, as I don't want to give away my personal info to every public network I may connect to.
Not every provider limits their users to a mere 64k upon exhausting the daily limit. The reduced speed ranges up to 256k on some providers.
True, but that's still slow, and given how slowly (or nonexistent-ly) the main site loads on 64 kbps under my experience, I expect it will still load fairly slowly on a 128-256k connection.