so if in this case the master node of the future, if deflation will continue. it can reduce profitability if the increased costs.
Not sure what you mean. For every block of 5 Piv, 90% (4.5 Piv) are distributed between masternodes and stakers according to PIVX's 'see-saw' mechanism, while the remaining 10% (0.5 Piv) is allocated to the PIVX budget (development, etc.). This stays the same regardless of transaction costs. MN profitability (in terms of number of Piv generated per unit of time) would decline if many more people operated MNs, but it will not be directly/deterministically affected (again, speaking in terms of number of Piv generated per unit of time) by fluctuations in transaction cost or the precise trajectory of inflation.
If PIVX becomes deflationary, it would mean, by definition, that the network is handling A LOT of transactions. Moreover, it would mean that PIVX itself would be getting rarer, which in theory would increase the unit price, increasing profitability in terms of $$ (not number of Piv) generated per unit of time by MNs and stakers.
Generally, master nodes are not very appreciated with zero protocol as there's no much transparency with this. It's good they're bypassing this.
Masternodes are not being bypassed. Stakers are the primary block validators on a PoS network, while masternodes are 'facilitators', offering an extra layer of verification, improving transaction time, and allowing the blockchain to be downloaded faster. Masternodes will also (I believe) play a role in enabling PIVX's decentralized exchange, ZDex, which is planned for Q2 2018. Currently, masternodes hold all voting power on the PIVX network, but masternode holders previously voted to give up this privilege in favour of a more inclusive community governance model, which will be implemented sometime this year (scheduled for Q3 2018 in the roadmap).
So masternodes' main job is to improve network function, not to increase privacy--though, a MN run through Tor might indeed add some extra privacy as a bonus. The privacy side of things is taken care of by Zerocoin protocol and, once implemented, other upcoming features such as I2P, U2F, and Dandelion protocol, all of which are included on the roadmap.