https://query.wikidata.org/sparql is the main instance which is used to query Wikidata. However, in some context, other instances may be useful. For instance, https://qlever.cs.uni-freiburg.de/wikidata/ is sometimes used to run big queries on a dump of Wikidata. Another instance is https://wikidata.demo.openlinksw.com/sparql.
I think it would be useful to add an instance parameter to wdqs_requester. Do you think it's a good idea ?