Unix doesn't need file extensions - although it can use them (in fact directories can have extensions!). Windows has some system files that don't have extensions - e.g. hosts and lmhosts files. There are several common Windows file extensions with only 2 letters - e.g.
JS.
So there's really no ticking time bomb!
People were predicting the end of the internet when available IP addresses ran out - that's what prompted the specification for IPv6 - but as things panned out CIDR and NATing effectively allowed millions of nodes to use the same IP addresses (i.e. 10.0.0.0, 172.16.0.0 and 192.168.0.0).
SD