Create SQL Column with Variable Default

I wanted to create an integer column in a metadata table that would prioritize the rows of the table (this is for column [execution_order]), and for ease-of-use I wanted inserts into the table to default to a unique value. Although this sounds a lot like an identity column, I wanted it to be nullable, and not necessarily unique.

This is what I came up with:

CREATE TABLE [dbo].[metadata] (
[metadata_id] int NOT NULL identity(1,1)
,[project_id] int NOT NULL
,[descr] varchar(100) NOT NULL
,[delete_stmt] varchar(max) NOT NULL
,[execution_order] int NULL
,[insert_date] datetime NOT NULL
,[insert_userid] varchar(50) NOT NULL
,[is_active] bit NOT NULL
,CONSTRAINT pk_dbo_metadata PRIMARY KEY ([metadata_id])
)
GO

ALTER TABLE [dbo].[metadata]
ADD CONSTRAINT df_dbo_metadata__insert_date
DEFAULT(GETDATE()) FOR [insert_date]
GO

ALTER TABLE [dbo].[metadata]
ADD CONSTRAINT df_dbo_metadata__insert_userid
DEFAULT(SUSER_NAME()) FOR [insert_userid]
GO

ALTER TABLE [dbo].[metadata]
ADD CONSTRAINT df_dbo_metadata__is_active
DEFAULT(1) FOR [is_active]
GO

ALTER TABLE [dbo].[metadata]
ADD CONSTRAINT df_dbo_metadata__execution_order
DEFAULT((IDENT_CURRENT('[db].[dbo].[metadata]')) * 100) FOR [execution_order]
GO