You can do something like this:

DECLARE @SQL nvarchar(max)
SELECT  @SQL = STRING_AGG(CAST(N'
select N' + QUOTENAME(name, N'''') + N' collate database_default AS [catalog]
,   ss.name collate database_default AS [schema]
,   so.name collate database_default as [tablename]
,   s.name collate database_default AS [column]
,   st.name collate database_default AS [type]
,   seed_value, increment_value, s.last_value
,   CASE LOWER(st.name)
            WHEN ''bigint'' THEN CONVERT(BIGINT, last_value) / 9223372036854775807
            WHEN ''int'' THEN CONVERT(INT, last_value) / 2147483647
            WHEN ''smallint'' THEN CONVERT(SMALLINT, last_value) / 32767
            WHEN ''tinyint'' THEN CONVERT(TINYINT, last_value) / 255
        END AS [RATIO]
from ' + QUOTENAME(name) + N'.sys.identity_columns s
inner join ' + QUOTENAME(name) + N'.sys.objects so
    ON  so.object_id = s.object_id
inner join ' + QUOTENAME(name) + N'.sys.types st
    ON  st.user_type_id = s.user_type_id
INNER JOIN  ' + QUOTENAME(name) + N'.sys.schemas ss
    ON  ss.schema_id = so.schema_id
where so.is_ms_shipped = 0
' AS NVARCHAR(MAX)), N' UNION ALL ')
FROM    sys.databases
where   state_desc = 'ONLINE'
EXEC    (@SQL)

It builds dynamic sql string which unions all databases and executes it once.

I simplified the usage of views so you use something a bit more modern, but you can probably adapt your original script from the general idea.

The query itself can be simplified a lot by querying the sys.identity_columns system view, which already contains table, column, last value, seed and even size information in bytes, in the form of the max_length column

For example :

select DB_NAME() As DB,
    OBJECT_SCHEMA_NAME(object_ID) as SchemaName,
    object_name(object_id) as TableName,
    name as ColumnName,
    TYPE_NAME(system_type_id) as ColumnType,
    cast(Seed_value as bigint) Seed_Value,
    cast(Increment_value as bigint) as Increment_Value,
    POWER(2.0,max_length*7) as MaxSize,
    cast(last_value as bigint) as Last_value,
    cast(Last_value as bigint)/POWER(2.0,max_length*7) as ratio
from sys.identity_columns;

The maximum size is generated by raising 2 to the number of bits. max_length*7 is used instead of max_length*8 because the question seems to only count positive ID values. Nothing prevents negative ID values though.

seed_value , increment_value and last_value are a sql_variant columns that must be cast to a numeric type before they're used in calculations.

This query can be executed against all databases using the undocumented but globally (as in used by everyone,everywhere) sp_MSForEachDB stored procedure

declare @sql nvarchar(2000)=N'USE ?; 
select DB_NAME() As DB,
    OBJECT_SCHEMA_NAME(object_ID) as SchemaName,
    object_name(object_id) as TableName,
    name as ColumnName,
    TYPE_NAME(system_type_id) as ColumnType,
    cast(Seed_value as bigint) Seed_Value,
    cast(Increment_value as bigint) as Increment_Value,
    POWER(2.0,max_length*7) as MaxSize,
    cast(last_value as bigint) as Last_value,
    cast(Last_value as bigint)/POWER(2.0,max_length*7) as ratio
from sys.identity_columns;'
exec sp_MSForEachDB @sql

This produces multiple result sets. These can be inserted into a temporary table or table variable:

declare @ratios table (
    DB nvarchar(100),
    TableName nvarchar(100),
    ColumnName nvarchar(100),
    ColumnType nvarchar(20),
    Seed_Value bigint,
    Increment_Value bigint,
    MaxSize bigint,
    Last_value bigint,
    ratio float);
insert into @ratios 
exec sp_MSForEachDB @sql
select * 
from @ratios 
Where ratio>0.001

All this can be wrapped into a stored procedure that returns rows that exceed the ratio:

create procedure large_identities(@ratio float)
as
declare @sql nvarchar(2000)=N'USE ?; 
select DB_NAME() As DB,
    OBJECT_SCHEMA_NAME(object_ID) as SchemaName,
    object_name(object_id) as TableName,
    name as ColumnName,
    TYPE_NAME(system_type_id) as ColumnType,
    cast(Seed_value as bigint) Seed_Value,
    cast(Increment_value as bigint) as Increment_Value,
    POWER(2.0,max_length*7) as MaxSize,
    cast(last_value as bigint) as Last_value,
    cast(Last_value as bigint)/POWER(2.0,max_length*7) as ratio
from sys.identity_columns;'
declare @ratios table (
    DB nvarchar(100),
    TableName nvarchar(100),
    ColumnName nvarchar(100),
    ColumnType nvarchar(20),
    Seed_Value bigint,
    Increment_Value bigint,
    MaxSize bigint,
    Last_value bigint,
    ratio float);
insert into @ratios 
exec sp_MSForEachDB @sql
select * 
from @ratios 
Where ratio>@ratio

And called with the ratio as a parameter:

exec large_identities 0.001