Typesetting a full citation whose title ends with a word in braces

This is a known problem (https://github.com/plk/biblatex/issues/295) and affects all in-text citations, although it is probably only ever really visible with something \fullcite-like. Unfortunately, the chances for a proper solution are quite slim. biblatex's punctuation tracker heavily modifies existing spacefactors, but doing so in citations can have unwanted knock-on effects for text outside citations.

You would have to add an \@ after capital letters in the end of a title. But you can have that done automatically for you in the format, if you like

\DeclareFieldFormat{title}{\mkbibemph{#1\@}}
\DeclareFieldFormat
  [article,inbook,incollection,inproceedings,patent,thesis,unpublished]
  {title}{\mkbibquote{#1\isdot\@}}
\DeclareFieldFormat
  [suppbook,suppcollection,suppperiodical]
  {title}{#1\@}

Dirty hack:

Insert something invisible with no width. I am sure this can cause problems, I just don't know yet which problems :)

\documentclass{article}

\usepackage{biblatex}
\makeatletter
\newcommand{\tempmaxup}[1]{\def\blx@maxcitenames{\blx@maxbibnames}#1}
\makeatother
\DeclareCiteCommand{\longfullcite}[\tempmaxup]
  {\usebibmacro{prenote}}
  {\usedriver
     {\DeclareNameAlias{sortname}{default}}
     {\thefield{entrytype}}}
  {\multicitedelim}
  {\usebibmacro{postnote}}

\usepackage{filecontents}

\begin{filecontents}{test.bib}
@inproceedings{blow2015,
  author       = {Blow, Joe},
  title        = {{GNU} loves me},
  year         = 2015,
  booktitle    = {Proceedings of Some Conference},
}

@inproceedings{blow2016,
  author       = {Blow, Joe},
  title        = {I love {GNU}\mbox{}},
  year         = 2016,
  booktitle    = {Proceedings of Some Conference},
}
\end{filecontents}

\addbibresource{test.bib}

\begin{document}
\nocite{*}
\noindent
\longfullcite{blow2015}\\
\longfullcite{blow2016}
\printbibliography
\end{document}