This is a short article on the topic of kissing the thumbs. It was written in the Monthly Urdu Magazine of Dar al-Ulum Deoband of the month April: http://darululoom-deoband.com/urdu/magazine/new/tmp/02-Taqbilul%20Ibhamain_MDU_04_April_14.pdf
It is a research on the statements of the Hanafi scholars surrounding this subject.
The research on the statement of the hadith scholars “la yasihh” (it is not authentic) is particularly interesting, quoting solid scholars like Sh. Abdul Fattah Abu Ghudda and Imam Zahid al-Kawthari that when this wording is used, it always means that it is fabricated and not that it could mean hasan, or weak, as the innovator Ahmad Yar Khan and other Barelwis have claimed.
The article also discusses the reliability of those hanafi books in which it is mentioned that the practice of kissing the thumbs is recommended.