I agree with your suggestion that there should be some SLA for the articles to be approved but I think due to lack of time, sometimes there is some delay in approval. Also if the article is quite impressive and conforms the rules of the articles, it is easy for them to approve, otherwise they keep it for pending by providing some suggestions to improve it further.
Hope the article by you will be approved soon. You can also write an email to webmaster at their email id firstname.lastname@example.org by requesting for the approval.
Pawan Awasthi(DNS MVM)
+91 8123489140 (whatsApp), +60 14365 1476(Malaysia)