I've not been making my own dynamic hair so I can't comment on that process, but I have spent some time recently rendering other people's in P8. 
What I've found in most cases is that I've had to dramatically increase the number of hairs and lower the settings for root/tip width for most groups before I start to get realistic results. This has had quite an impact on render speeds.
This may not be much of an issue for lashes since they cover a relatively small area, but IMO you're going to need to really experiment with the hair room settings and make test renders at high resolutions to ensure a good quality result. I know I've seen one or two attempts at this for other figures (although I can't point you to any examples) which have fallen short for one reason or another - probably lack of knowledge in the hair room.

I do think it'd be well worth the effort though, at least as an option. Dynamic hair is really starting to come into it's own with P8, and yields far superior results. IMO at present it lacks the input of those with enough skill to make it work well in terms of creating it - they're definitely out there but possibly lost patience with the ability of previous versions of Poser to render it fast enough.
Dynamic clothing also seems a struggle for many.

 

PoserPro2014(Sr4), Win7 x64, display units set to inches.

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