I think it is safe to say the odds of this Al cover going into production which were below 25% from the day of the announcement are negligible at this point.
There have been pages now of wondering where Estel has gone in the sunset years of the N900.
For example, the only way I ever got the no-show 'like new' phone I bought from Estel was to reverse my paypal payment, a few months after the reverse a beat up barely functional N900(failed and unflashable 3 months later) arrived and I ended up having to pay paypal back and they paid estel $250.
Consider any money contributed to the project to be lost, as a one off maybe Estel has an Al cover, nobody, including those who prepaid will get a cover unless they have a lever to use on Estel.
Even if he did reappear and arrange a run on CNC I would expect him to deliver a rough cut with no finish or spraypaint.
Estel was once a good source of N900 hacking info, but he is gone from TMO, as are the always unlikely dreams of a cover which probably would have made using the phone as a phone(RF blockage) difficult to impossible.