Thats pretty much impossible keeping 1MB and increasing the number of people using Bitcoin. But if someone proved it is possible put to 1MB several times more transanctions and the solution is secure (from possible attacks) and convenient for Bitcoin users plus no centralized service is needed, then 2016 is the latest year it could be tested whether it works. As I understand LN can not be the only solution because it is not convenient for Bitcoin users to have coins locked for longer time, but it can add to maybe -20% ? of the blockchain usage if LN gets popular - clearly not enought. But I pretty much doubt magic is possible here if we think about increasing Bitcoin usage at least hundred times in next 10 years and I dont understand the need to defend 1MB when Litecoin proved 4MB is fine for every 10 min from the security point.
1/ please provide empirical data as to any increase of bitcoin user base
2/ please provide technical details as to how relevant would the block size be when it come to scaling bitcoin effectively
3/ please provide evidence as to how increasing the blocksize would not lead to further centralization of the network.
until then, it is the contrary that prevails as bitcoin works perfectly fine as of now.
and you can keep the "pretty much impossible" for yourself.