The sequence could not really be removed because it defines the access right to its sequences. (This could be done by it will require to create a record rule for each new sequence type, so not more developer friendly).
But now we can use direct link from the sequence to the sequence type instead of using "code" string. This will enforce data integrity at the database level.
As we would remove the "code", the "get" methods can no more support a domain as parameter. This feature was almost no more used. Since years we have moved to an explicit configuration of the sequences.

For me there is no added value by the sequence type. Indeed it makes even more complex for developer to define new sequence.
I think we can just replace it by a usage Selection field directly on the sequence. This will also avoid a join to the table.