Do you mean something like what zigbee2mqtt
does? I'd love to see this!
Another option like other commercial gateways (Aqara, Tuya, Ikea etc.) wouldn't add anything to the market but another incompatible system. Every manufacturer has his own line of products with own cloud and nobody wants to have multiple Zigbee gateways at home. Also it sucks if your fine-tuned heating system stops functioning because your ISP has few hours unavailability.
Unfortunately zigbee2mqtt is written in node.js so porting it to RouterOS would be impossible considering limited resources available on most Mikrotik hardware.
I'm afraid that developing and maintaining own solution would be too resource consuming for a company that has plenty of work in backlog like Mikrotik has.