This is a very good question. I had to think about this awhile. The word "some" is usually an article like "a", "an", or "the". In English, we never put an adjective before an article. If there is an adjective like "new", it should be between the article and the noun. We say, for example, "the new thing" but never say "new the thing". So... even though "some" is combined with "thing" to form its own word which is a noun that should be able to have an adjective before, we never do that. You can say "some new things" but you can't say "new some things".

I'm not a teacher but I believe in this case, 'something' is being used as an adverb, not as a pronoun. 'New,' as an adjective, would normally come first however in this case 'new' is acting as an adverb to add emphasis to 'something.'

It is one of those english things that just doesn't sound right. You would need to use an article to swap it around first of all. You could say "I learned a new something today." but it just doesn't sound natural. It would be best to use "I learned a new thing today." if you really want to put new first in the sentence.