Currently the index has “List of registered (limited liability) companies”. However this does not include NPO/charities in many countries. (For UK/US IIUC, charities are companies with special recognition, so they are basically already companies)
Do people think that the index should include all legal entities required for registration in each country?
In my opinion - not in this stage, maybe in the future. Charities are important, but as you said, they are different legal entities. In some countries these are two different datasets and not a consolidated one. In general i believe that taking example from UK / US will not be helpful when benchmarking other countries, specifically global south one.
Also, there is still so much work to do on company register data in many places in the world, that adding charities data with it might cause confusion.
Having said that, I noted it for the next dataset public consultation for the Index. Maybe other wants this data as well. 
One of the reasons we want company registry is to effectively link spending data and contracts. However in many cases the vendors or bidders are NGOs or government-sponsored NPOs (or even universities) that are not in the company registry.
yes a separate scorecard for charities/ngos/etc could be useful, websites and facebook pages often still do not include reg no in footer or in about
avoidable hours to code some IATI datasets!
an assumption of extra scorecards each year would keep top 20 on their toes and certainly help maintain funding/progress ;0)
This is a solid point. NGOs are allowed to bid in government tenders and they may partner with government in projects. In many countries governments use GONGOs to pretend some kind of civic dialogue.
But the type of information relevant about NGOs may be different than the one for companies. Thus, it makes sense to discuss about a separate item rather than one that includes both categories.
Registered Charity Organisations added to Open Data Index Consultation.
Add you votes for your favourite datasets - vote as much or as little as you like.