Just like we have alternative characters for the letters "a" and "g" in the Latin script. Although they are not necessarily required, they do make the font richer and enable the intended users to have more choices. In the same way, we have a bunch of alternatives in the Devanagari script, too.

Source :
https://www.typotheque.com/articles/regional_forms_of_devanagari_survey_report

The website clearly mentions the regions where these variations are used. Because of the requirements of the Marathi and the Nepali languages, it is good to see Noto Sans Devanagari already contains the alternatives of ५, ८, झ, ल, श. But I urge you to add alternatives for the other mentioned letters as well.

Furthermore, although I am aware that the Noto Devanagari is designed for general purposes for Hindi and other commonly used languages. But since Noto Devanagari is one of the most interacted Devanagari fonts, if not the most, along with excellent Devanagari Unicode support, I genuinely urge you, for the intended users, to add support for proper rendering of the Vedic Extensions and, for the Sanskrit language and others, consider adding vertical and complex ligatures as "alternative glyphs". Since they do require a lot of time and hard work, it is totally up to you to add support.

The following PDF has a bunch of ligatures contained in the Chandas font, which would be preferred for the Sanskrit language :
http://www.sanskritweb.net/cakram/saMyoga-pattra.pdf

As I mentioned, these are not necessarily required, but they will make the font richer and enable the intended users to have more choices :)