Itch does not work on the principle of Patreon and even Steam. If the price of the game rises (for example, the price was $5, and then changes to $10) - then according to some laws itch - those who bought the game for $5 - will not be able to get files for $10. We do not set these rules, these are the rules, etc.
On release, the game will most likely cost $10. If you buy the game for $10 now (namely, pay $10, not $5, but exactly $10) - then on release you will get the game on itch without any problems.