According to this document: https://docs.google.com/document/d/1Xf_iHGI51Lp6nVHPZo0SdUw60-NA6YJUvk2s-eYaxLE
maxDeposit - the maximum deposit allowed to become a proof of stake validator. If you want to deposit more, you must purchase multiple slots. Set to 50000
Alongside this, another question is how to target the minimum entry size and a possible entry fee. One approach is to auction entries, thereby resolving many preference revelation issues and allowing targeting a fixed PoS participation rate, but at the cost of introducing or exacerbating selfish-mining attacks.
Looks like there is a talk about to make paid participation. And maybe there be a market of participation. With which, I'm, personally, perfectly fine and I think this is very good thing (see conversation in this question).
The path how I found it was: Ethereum documentation --> Other Ethereum Links: Giant Ethereum Resource List --> Proof-of-Stake Resources: Vitalik's CASPER Spec Google Document
Can't be sure is it relevant now.
So is there such a plan?