I can think of several reasons why Concept2 would be reluctant to go external hardware only.
First would be the need to write drivers to support the dozen different OS's out there for Android and iOS. With their own hardware (or, with a vendor they are working with) they know the chipset, and they know the hardware. From an embedded systems background, this is why they will stick with providing their own monitor. No guesswork.
The next reason is now they have to sell the machine to someone who might not want to plug in their phone. People are very, very fickle. I'd say dumb, but I don't want to get slammed. Once they remove the hardware, they are now on the hook for supporting a bunch of calls from people that complain their phone doesn't sync up with the rower...because they forgot to plug it in. Or if it's bluetooth, because they don't have bluetooth turned on their phone. Now they have to have staff asking "Which phone do you have? Which OS? So your phone worked fine yesterday, but it updated last night, and now it doesn't work?
"
Or worse, they didn't download the software from the Concept2 site because some malicious third party software vendor rigged the google SEO so
their site comes up before C2, and their site is nothing but an ad driven piece of crap that also comes with a monthly subscription. Now Concept2 starts losing their place in the market as the undisputed king of ergs with stellar support, all because they tried to save a buck on some hardware.
Gyms will have people rowing away, oblivious that there are metrics that come with the rower with no display, because they didn't know they could put their phone in the cradle and have it give useful feedback. And again, that's if C2 decides to integrate bluetooth on some hidden piece of hardware.
The can of worms that you are asking them to open, they won't open. As a third party software vendor, they were very helpful to me. They want to stay in the exercise equipment business; supporting software, even something as simple as a device driver, is not something they, or any company, can afford to do. As you know, Carl, the number of people erging and using Rowpro is a small percentage. The best they can hope for is developing an interface for something like Unity, which would allow all the cross platform software headaches be placed at Unity's doorstep.