All regular format DVDs are recorded in 480i, and were always meant to play in 480i. They only appear as 480p after transcoding, which takes place these days inside the DVD player itself before ever leaving the player. Same with upconverting to 1080i, the upconversion happens best inside the digital domain before it ever leaves the player, and all Bluray players currently available upconvert the regular DVD 480i to 1080i if you wish, you just have to tell it to do that in the player's menu, as to what's the highest scanrate you will want your content to be playing in, whether it comes from 480i DVDs or 1080i/p bluray discs. Which for our sets will be 1080i, not 1080p.
Only catch is, the UPconversion to 1080i from 480i has to leave the player as HDMI. Not component, which is limited to 480p on upconversions from regular DVDs.
In yesteryear, you had to have a DVDO or Faroudja or whatever other scaler, to upconvert the 480i to 480p. And to 1080i. These days all you need is the conversion from HDMI to component, which is what works best in our sets.