I was afraid that the number of full nodes may decrease drastically taking into consideration the size of the blockchain which is technically too high for a hard disk of a PC.
I think you meant HDD speed, not HDD storage. Blockchain size is only 250GB which is small compared to today's customer HDD capacity (0.5 - 8TB)
It would be great if some solution could be implemented to speed up the synchronization because it would be only worst during the time.
At least for Bitcoin Core client, there are many optimization on synchronization. The biggest hurdle now are using HDD to store Bitcoin's blockchain or/and slow internet connection which hardly can be optimized.