It's likely that much greater capacity at all possible pinch points has been incorporated, and financial provision made to fix any unexpected bottlenecks very quickly indeed in the early days. It won't just be a wodge more fibre cabling.
It was just a point to bear in mind though. I doubt if in reality you will see much, if any, degradation when they switch fully to it.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. 200GB. Sync 76102/14089Kbps @ 600m. BQMs - IPv4