"We live in an interesting age" or so the quote goes. It is very interesting that BGI are going to start selling sequencing technology. The coverage of Jun Wang's (BGI CEO) JP Morgan presentation by GenomeWeb lays out what they plan to do to start actively competing with Illumina: exome sequencing, NIPT on BGISEQ-1000 and now new sequencers that will compete directly with HiSeq and MiSeq.
I am not sure, but would hazard a guess that BGI is still one of Illumina's largest customers for instruments and reagents. It must be an interesting relationship to manage from both sides!