sorry, you're wrong again. mara slipstream is currently in operation and can be accessed here:

Slipstream | MARA Holdings, Inc.

here is an example of a nonstandard transaction that they included recently. it was never in the mempool.

The Mempool Open Source Project®

Explore the full Bitcoin ecosystem with The Mempool Open Source Project®. See the real-time status of your transactions, get network info, and more.