Well it doesnt have to be upgraded perse but i want something that can handle faster speed as the 251 is only 1000mbps and the only way to upgrade to get it to 2.5GbE will be with a USB wifi dongle and i want to be able to hardwire it to the network instead of WiFi.
And i also want to upgrade so i can add more storage on the same NAS instead of adding external storage. I am going to still use the 251 to run other things that i didnt want to run before because i wanted it to solely be a PLEX server. My daughters and son live far from me and the grandkids so they stream a lot from me so i want to take advantage of the upgrade with fiber.
I know i can add bigger HD to it and i already did but like i said before the 251 will be used for other things and again the new NAS will be my plex server and will also have home assistant moved to it as well as being the point of backup for my computers and phones including the grandkids phones and my kids.
The main reason to upgrade is to have more space and speed as well as being able to run other things i have been running in the cloud.