I have some data that isn't properly "partitioned" (for lack of a better word).

All inserts, processing and reporting happen on the same table. The bulk of the processing happens not long after the insert and not long after that it becomes immutable (we're talking days).

I could do all inserts and processing on a new table that I replicate to the old table. When I detect that the data has become immutable I would delete the data from the new table, but I would edit the delete replication stored procedure so that the delete did not replicate.

How bad an idea is this?

It seems attractive at the moment (I haven't slept on it yet) because it might mitigate a performance problem with only very small changes to the application. It also seems like it might be a good way to shoot myself in the foot.