While I like the concept to enable the ecommerce component to be multi-tenable as well, I would like to point out the following:
eCommerce front ends (webshops) are intended for specific target audiences. This means that UI and UX are of the utmost importance. While this extension of functionality caters to that partly (providing the different domain), it often involves more than just this.
Not only difference in theme, but also heavily customizations in layout structures through screens, forms, groovy and ftl files. Often this means a new e-commerce application per target audience.
Keeping such in one component increases the risk that changes in one eCommerce front end bleeds into another.
Having front end applications in separate copies of the ecommerce component (whilst reusing all the services, etc), specifically developed for each tenant and associated to the tenantId reduces that risk significantly.
Also if I recall correctly, handling of different domain names is already implemented in the content mgr component and can be used for multiple domains in an implementation. Thus also within a multi-tenancy setup.
Are your changes with respect to this really required?