Hi,

the following example, which uses a \fontspec statement in a tabular
column declaration as per >{}

\listfiles
\documentclass{article}
\usepackage{fontspec}
\usepackage{array}
\begin{document}
% \begin{tabular}{>{\sffamily}l}% works
% \begin{tabular}{>{\fontfamily{lmss}\selectfont}l}% works
\begin{tabular}{>{\fontspec{Latin Modern Sans}}l}% fails
  text
\end{tabular}
\end{document}

breaks with the following message

> luaotfload | cache : Lookup cache loaded from C:/texlive/2015/texmf-var/luatex-c
> ache/generic/names/luaotfload-lookup-cache.luc.
> luaotfload | load : Lookup/name: "Latin Modern Sans" -> "lmsans10-regular.otf"
> luaotfload | load : Lookup/name: "Latin Modern Sans" -> "lmsans10-regular.otf"
> Runaway argument?
> {\__keys_if_value_p:n {required}\unskip \relax \d@llarend \hfil \hskip \ETC.
> ! Forbidden control sequence found while scanning use of \bool_if:nTF.
> <inserted text> 
> \par 
> l.9   t
>      ext
> ? 
> ! Emergency stop.
> <inserted text> 
> \par 
> l.9   t
>      ext
> End of file on the terminal!

when compiling with

  * TL2015 (up-to-date)
  * TL2014 (indefinite update state)

The example compiles fine with

  * TL2013 (indefinite update state)

Traditional NFSS style font commands within >{}, such as \fontfamily,
work in all three TL versions.

Log files (of successful runs) containing file versions are attached.[1]
 System is Windows 7.

Best regards,
Stephan Hennig

[1] As archive since I exceeded mail server's 2000 lines limit when
sending uncompressed.