Specifically, the SEs (and therefore test statistics) will be biased because estimated factor scores will be treated as known/observed data.
There is also an analytical alternative that should be more efficient (both less computationally intensive and smaller SEs because the plausible-values approach has additional Monte Carlo error; this is analogous to comparing multiple imputation to FIML). Unfortunately, the fsr() implementation in lavaan is very "beta", not yet ready for public consumption (research still needed to reveal the wisest default options). But when it is, we might never need to simultaneously estimate these big SEM models again :-)
Terrence D. Jorgensen
Assistant Professor, Methods and Statistics
Research Institute for Child Development and Education, the University of Amsterdam