Oh, that's interesting!
Sadly the machine only has one SD-card slot, so we won't be able to have 300 sounds at our fingertips in one go ;)
(When you say "thirdsound card", I guess you mean "second" (the first 100 voices are in the internal permanent memory, not on a card...... unless Markus did a second card while I wasn't looking!).
The first expansion card already had all the Mk1 & Mk2 rhythms, though?
It also had more than one duplicate sound.... and stubbornly omitted my favourite sound (the M400 string section).
When I saw Markus in person at Musikmesse 2012, he told me the first card was "ready" and I sent him the cash by paypal the next week, and it still took several months before he was actually able to ship... so when he says "at the end of the summer it will be available" I have to smile and wonder which summer ;)
But basically this is good news :)
Purists may look upon it as a splendid way to audition and choose which real tape frames they wish to buy for their real mellotron ;)
David