In my opinion and ...

In my opinion and experiences across areas I have had the privilege of visiting - the level of appropriateness per application should define the basic sanitation application. I have seen many inappropriate applications where the "poorer of the poor" are provided with services that fail, and some that function, however. On-site sanitation (pit latrines, UD, self composting, et al) are likely to be basic sanitation applications although, again in my opinion, they do not seem to be appropriate for various reasons, inclusive of odour generation leading to vector attraction and as a result elevated sickness and disease, safety both personal and structurally, groundwater contamination, maintenance and no real opportunity to recover and recycle water for sanitation.

So perhaps, if one considers the advancement of simple waterborne sanitation systems, this could still be a more appropriate application, albeit at single household level. Yes water supply and power will more than likely be necessary, but technologies are available to apply this and the treated effluent can be utilised for recycling and/or re-use as applicable.

Community engagement, education and acceptance of any "basic sanitation" application is key to sustain that function, again sometimes an activity that is overlooked by decision makers. Water drawn from wells in remote regions are being paid for by these communities, so cost recovery is not insurmountable, but indeed will be sensitive. What is affordable?

So perhaps the term you are seeking to define should be sustainable, appropriate basic sanitation - and I would expect this to not be a general definition but variable according to region and application