Unless you have a way to ensure the code actually running on voting machines is the code that was published, there is no point.
Right now if there is a bug that creates incorrect vote totals it would be very hard to prove it was done intentionally. If the software was required to be open source, then just the fact that they were running different software than was published would be strong evidence that it was intentional.
>> ... will be fitted with a printer that will have a drop box to store the paper trail of the votes cast. This is expected to alleviate concerns — expressed earlier by the opposition led by BJP — over possible tampering of EVMs to favour a certain candidate.<<
http://www.business-standard.com/article/pti-stories/2019-ge...
http://timesofindia.indiatimes.com/india/EC-ready-with-new-a...