In the D&D 4e Monster Manual, there are monster templates such as 'lich' which increase a standard monster to elite or an elite to a solo.
Do monster templates still appear in more recent core D&D material?
Yes, templates are still being published
Page 117 of the Neverwinter Campaign Gudie has a Wererat template.
Interestingly, unlike the templates in the original core products, it does not make the monster an elite.
Futhermore, this Book of Vile Darkness preview article presents a Moilian Dead monster theme, which has a lot in common with monster templates (the key difference being DM choice in picking theme powers from a menu).