The point is that with bitcoin (in the endgame, when it is more stable and super user-friendly) they won't have to buy stocks, bonds etc. to get the same benefits that fiat delivers today.
That is why a "business plan" is needed. Obviously, the purchase power of bitcoin cannot keep growing 1000% per year forever. When it stabilizes, will bitcoins appreciate more than stocks, or less than stocks? If more, no one will exchange their bitcoins for stock (so how would new companies start, and where will all the holders' revenue come from)? If it starts growing less than stocks, then people will want to exchange their bitcoin hoards for stocks, and price will drop, maybe 90% or more, untill all the 21 million coins are in circulation. Will this be the case, or will bitcoin appreciate just as much as bonds and stocks? The "business plan" would have to pick one aleternative and show that it is consistent with teh rest of the model.
However there are fees associated with moving in and out of bonds, stocks etc. . If you want to buy and sell bitcoin on an exchange now, there are also fees associated with it, but when more people use it for buying their pizza, paying out salaries etc., this won't be the case.
Depending on the date of the "endgame" and the guessed price of bitcoin then, mining may not be enough to sustain the network, so the transaction fees will be mandatory. The "business plan" would have to guess the transaction volume, pick a percentage for the fees, and specify the difficulty level that matches that. (Depending on the fee structure, paying a pizza with bitcoin may or may not make sense.)
One complication is that there may be banks and/or credit card companies offering payment services in bitcoin, possibly with smaller fees (being centralized, their porcessing costs would be much smaller than bitcoin's) and/or other advantages (like lending, cancellation, insurance, etc.) But payments made through them will normally be accounted in their internal ledgers, not in their blockchain (like, as of now, most dollar payments made through banks do not involve dollar bills). Those intrabank payments will not pay bitcoin transaction fees. So, in order to establish the bitcoin demand and fees, the business plan would have to identify the fraction of payments that will be made through the blockchain, and may have to pay higher fees than bank transfers.
I know that all these issues have been extensively discussed, but I have only seen them addressed one at a time, and I wonder whether the "solutions" that have been presented for them in isolation are compatible with each other. (For example, I recall one famous advocate claiming that people would pay coffee and groceries with a blockchain app on their cellphones, while another claimed that bitcoin would be used only for expensive items like cars or real estate, another wrote that it would be used only for transactions that need to be hidden, and yet another that it would be used only for inter-bank settlements...)