Hi Gumbork. Ultimately the number of blocks are dependent upon the number of cards bought by players. Given the size of Block 2, this could be -- and this is an estimate -- between 500k and 2m cards. Once those cards have been sold, it becomes more expensive for players to buy cards from that block and we will offer cards for sale from the next block at the regular price.
Having fixed blocks (instead of an endless supply from one infinite block) allows for an ongoing iteration of new card properties and abilities. A lot of CCGs do this -- Magic, as an example, issues 2-3 core "sets" per year. I expect that we'd be looking to adjust the size of blocks to the ongoing demand for cards. As the player base increases the blocks get larger to anticipate demand.
For the first few blocks we've intentionally kept the size small (2m cards isn't very many when you consider that average players may have 250 or more cards in their collection). Because of this, we're being careful to only release block sales as and when we're ready (especially as we've not launched any games yet). At launch of the block system we announced blocks 1 and 2. Block 1 is fully sold and block 2 is over 70% sold now, but as it currently stands we haven't sized Block 3. It's likely that there'll be a gap between blocks 2 and 3.
G.