The Olympic line was originally designed to be part of Line 10 — and was supposed to be this tiny bit that jutted into the north. There wasn’t really much use for the line, apart from two months of Olympic fever in 2008. The 4 km-ish Line 8 has every potential to become a real Subway dragon, with all extensions in place.
Ah. Here’s the good bit. The Olympic line was renamed Line 8, stripped of its Olympic-only name, and became a separate line. The newly-renamed Line 8 then took a life of its own — with extensions further north and south to come long after the Games were finished.