Frankly, without looking at it OSRS gold directly, it can be told based on what it's advised to us. Chat platform, friends list, and the friends talk is a large one. Then there is the payment method, it is possible to just have 1 payment going on at once for your own account. So, if you buy membership through bonds on both, say for example, it might conflict. Your account is split, to an extent.

You've got your Jagex account, and also the individual game's account (profile). You jagex account handles which sport you're playing, which planet you're on, membership status, ban/mute standing, etc. (You could just play RuneScape, or one FunOrb game for example in the past).

Certain items, such as your character name, is handled in the Jagex accounts, rather than RuneScape game profiles. Unlike bank pins, that are specific. So, really, they would have to change and convert things over to allow multiple systems, to work in matches. Instead if just allowing the connection, and hope for the best, proceed from there, and they will have to modify their communicatuons between the two. They will have up upgrade each system that uses it Should they alter a system in the platform. So, both osrs and Runescape, would need to upgrade to use it.

The RuneScript engine involving both are different. So the how to make money in old school runescape scripts demanded for specific sub-systems may differ slightly, so 1 game may be able to add support for exhibiting numerous worlds and chat channels, whereas another may need to rework a lot to do so.