To what extent does this happen with Ethereum, and won't it mean that distributed applications will basically become unworkable at some point in the future?
To what extent does this happen with Ethereum, and won't it mean that distributed applications will basically become unworkable at some point in the future?
Completely untrue. Difficulty is proportional to the hash rate. Transaction time varies as a result of multiple factors.
Some reading and historical difficulty/confirmation time data:
https://blockchain.info/charts/avg-confirmation-time?timespa... https://en.bitcoin.it/wiki/Difficulty http://bitcoin.sipa.be/ https://en.bitcoin.it/wiki/Confirmation#Confirmation_Times
If you're interested in scaling approaches, Vitalik Buterin has written a lot about this issue in a very thoughtful manner, both as it applies to Bitcoin and Ethereum.
The best estimate is that the last block will be mined around 2140 based on the block reward halving frequency of four years. According to math and knowledge that there are 32 halving events, in 2136, the block reward will yield 0.00000168 BTC per day, which is 0.00000042 BTC per block.
We will all be dead ;) but to answer your other question yes transaction fee's will continue to incentivize miners but who knows where the protocol will be by then. It could be completely changed.