Is it possible to use spike-ins with droplet technologies? By reading Bacher &amp; Kendziorski (2016), I found the following statement:


  recent droplet technologies are not yet able to accommodate spike-ins


What's the reason why current droplet technologies cannot use spike-ins? By searching through the available methodologies I found this question on 10X community, but still I cannot understand what is the problem created by using spike-ins with droplet technologies.


Bacher, R. &amp; Kendziorski, C. Design and computational analysis of single-cell RNA-sequencing experiments. Genome Biol. 17, 63 (2016).
I believe it is mostly a cost issue as spike-ins are "expensive" to use given the large number of cells that are/can be sequenced via droplet based methods (as compared to plate-based ones). The 10x link that you provided actually states that this is possible with 10x and Klein et al. used ERCC spike-ins in 953 droplets (Cell. 2015 May 21;161(5):1187-1201. doi: 10.1016/j.cell.2015.04.044.).