The extension shouldn't be limited within 10 years but also as a lifetime process, not just accumulating for 10 years only. The process is for us to look in a long run, DCAing, sticking to our investment plans also not over engaging the process but developing a system that makes you consistent in your accumulation phase. If we treat it this way, we won't get tired but keep investing in our digital gold.
Its not out of place to invest in a much longer time (more than 10 years). Actually you can invest for as much as you desire, but why the pointers are between 4 to10 years is for your investment to be profitable for you, so you don't buy when the price is higher and sell in the dip. That's surely a loss. With that time frame, you'd have seen good gains and can decide for yourself whether to continue, or take your gains and quit. Bitcoin is always there to welcome you whenever you choose to return to investing, just that your gains wouldn't be compared to the one who perseveres for a longer time, maybe up to twenty years or more.
I'll advise that even after 10 years and you must've gotten your good profits, don't sell off, you can take of some part of your gains and invest into something worthwhile as a means of diversification, maybe agriculture or open a business that will continue catering for you so your investment remains untouched for another length of time and who knows, your investment can boom more than you expected and would provide you more funds to keep accumulating periodically. The goal is to keep increasing the portfolio for bigger and better profits.