Assuming that Eth will reach the hard cap (30000BTC) at IPO, there are about 30,000,000-60,000,000 eths sold in total (Let's take a median value 45,000,000). Considering 50% premine, the amount of eth should be 1.5*45,000,000 ~ 67,500,000 at launch.
Until 2070, the total amount of eth should be 67,500,000*(1+0.4*46)~ 1,309,500,000.
So just don't worry about the inflation. The amount JUST increase about 20 times in 46 years.
It's only a bit, isn't it?
This type of fundraising puts investors in a very bad spot. Right out the gate, miners will be reducing their value very rapidly. Exactly 1 year after, devs/founders will dump 1/3 of their stash.
So investors will have to fight just to retain their ROI... not a spot you want to put yourself in when investing in any other coin could give you hundreds of % easily (if you pick the right one). Not to mention, in 46 years, your initial stake will be diluted to 5% of it's original value, so holding for the long term is not particularly rewarding.
And my question of why ETH should have any value has not quite been answered. It's not being put forward as store of value, ETH's value is in the programs that can run on top of ETH. So they create a situation where most people won't actually buy more ETH than they need to run a particular program (ie. no one is going to want to hold ETH with these initial inflation rates and risk of devs dumping 1 year out). Why hold ETH when you can hold other coins, make a killing from price increases, and simply send a few dollars over to ETH if you happen to need to run a script? Why take a risk with the rapid inflation that may or may not devalue your original stake by -66% one year from IPO? 1-(0.5/[(0.5/3)+0.5+0.4])
In the beginning there will be very few programs to run and a lot of ETH available... perhaps it will be better to buy (and mine) after launch. ETH is a good idea, but they punish investors much too greatly.