I don't think the speed of text messaging allows for many other meaningful data types. Someone encoding video into the GSM-7 format used by SMS will still consume more data than the typical person typing and sending text messages (which is what, 140 bytes each way per minute on average?).
There is also the difference between free and paid. Sure, if you're paying, you should be able to do whatever you want at the advertised speed and data limits. But for a free feature, I think it's alright to limit to SMS and other texting apps (already done on inflight wifi and it works just fine).
Why not just limit to SMS? Because travelers' home carriers might levy roaming charges on SMS, and WhatsApp / Telegram / iMessage is already de facto in most of the world.
There is also the difference between free and paid. Sure, if you're paying, you should be able to do whatever you want at the advertised speed and data limits. But for a free feature, I think it's alright to limit to SMS and other texting apps (already done on inflight wifi and it works just fine).
Why not just limit to SMS? Because travelers' home carriers might levy roaming charges on SMS, and WhatsApp / Telegram / iMessage is already de facto in most of the world.