Every new skin should have an on release border, and here's why.
I'll take you back to the Super Galaxy event, which introduces the new pilots Gnar, Annie, Nidalee and Elise. Except... none of them have borders. I'm mainly looking at Annie for this one.
Annie had not received a skin since Hextech Annie... released in 2016. Instantly, you'll say: "Annie has a bucket-load of skins already." That's where I mention that Annie has 12 skins. Only 4 of them are available to buy. Leaving 8 skins to be untouched. Secondly, Annie's only border skin is Annieversary; which barely counts since it was given in celebration of the 10th Anniversary. So the last buyable skin on Annie before Super Galaxy was Panda, which was released back in 2013. 3 years between buyable skins and Annie still doesn't get a border.
Now, lets zoom to the present. Mecha Kingdoms; a COMPLETELY new skin line drops with borders for Sett, Draven, Jax and Leona. Guardian of the Sands; giving skins to Janna, Rengar and Ryze have no borders. Ryze suffers the Annie clause, having 12 skins with only 4 buyable.
Dunkmaster Ivern, no border. Beekeeper Singed, no border.
If you completely dedicate yourself to a champion, and you drop a ten on the skin that drops for your champion directly on release; you SHOULD get a border, regardless if the skin is Beekeeper Singed or True Damage Prestige Qiyana. And don't hit me with the "then the border loses its rarity." If you wait for a skin on a champion who hasn't received a skin in a while, ESPECIALLY when all their other skins are legacy locked; you deserve to get a border. Make it a "first day" border, separating them from skin group borders. ( Like how Prestige Borders are not like True Damage borders. )
Since you'll be focusing on older champions with skins this year; there BETTER be borders for ALL OF THEM. Especially Taliyah, since that special 1% who play Taliyah are biting at Riot's ankles.