Are you interested in adding support to your app for them?
Yeah of course. Adding support for another device that streams is only going to be a couple of lines of code to deal with the packet format, or any bazar ascii chars the manufacturer decided to throw at it (and how you interrogate the device to get what function it's on, and range). However if a device doesn't "stream" its readings, and needs to be polled, then that's a bit more work.
Bluetooth is easy and cheap. It also has the advantage that you only need the two devices to work easily. It's also been surprisingly robust on my bench. However, TCP/IP via WiFi is also an option that could be used, and it looks like you can get modules off ebay for around $15ea that have RS232 output. From the viewpoint of the Android device, it's very similar to work with. Just a slightly different setup, i.e. look for an IP address instead of a pair device.
Most of the work from the app perspective is in getting the charts to display how you would naturally expect them to with all input conditions. This actually isn't trivial, and requires a lot of manual code intervention to get it all to look right. So yeah, adding more devices and/or features it the relatively easy part. At first I'll be looking at everything the 34461A can do as a starting point for features.