I've work on projects where we did it the opposite way, with multi-tenancy as the default. It didn't work. For a couple customers, we had to carve out their own dedicated resources. A few of them were absolutely murdering the performance of the rest of the cluster(s), and some had business requirements to be completely isolated. Customers with similar requirements and workloads we kept in a multi-tenant pool.
Even though some of the benefit of multi-tenancy is (supposedly) simpler management (one set of resources), multi-tenancy can actually become more difficult as the customer pool gets bigger, or workloads get more uneven. Maintenance on the whole pool becomes more and more problematic, and you try to patch around or delay it by scaling vertically. You basically run into every possible problem and hit limits you hadn't thought of sooner than with single-tenancy. And worst of all, it's impacting more and more customers.
Even though some of the benefit of multi-tenancy is (supposedly) simpler management (one set of resources), multi-tenancy can actually become more difficult as the customer pool gets bigger, or workloads get more uneven. Maintenance on the whole pool becomes more and more problematic, and you try to patch around or delay it by scaling vertically. You basically run into every possible problem and hit limits you hadn't thought of sooner than with single-tenancy. And worst of all, it's impacting more and more customers.