Yes, I agree that there will be gaps in the sequence and also multiple users might update the same record. But don't you think the gaps would any way be there if for instance a sequence is used (as a feature of Sql Server 2011) as the first choice by the author and later on the transaction is rolled back.

So, I would not consider that having gaps in this case an issue which also moots the problem of updating the same record by multiple users.

My main focus was on removing the blocking issue.