Deprecate no-op transpose fallback instead of error'ing.

base/deprecated.jl

@@ -784,6 +784,15 @@ function symperm{Tv,Ti}(A::SparseMatrixCSC{Tv,Ti}, pinv::Vector{Ti})
         "Pkg.add(\"SuiteSparse\") to install SuiteSparse on Julia v0.5."))
 end
 
+# Deprecate no-op transpose fallback. Please see #13171 and #17075.
+function transpose(x)
+    depwarn(string("the no-op `transpose` fallback is deprecated, and no more specific ",
+        "`transpose` method for $(typeof(x)) exists. Consider `permutedims(x, [2, 1])` ",
+        "or writing a specific `transpose(x::$(typeof(x)))` method if appropriate."),
+        :transpose)
+    return x
+end
+
 # During the 0.5 development cycle, do not add any deprecations below this line
 # To be deprecated in 0.6
 

base/operators.jl

@@ -293,7 +293,6 @@ fldmod1{T<:Real}(x::T, y::T) = (fld1(x,y), mod1(x,y))
 fldmod1{T<:Integer}(x::T, y::T) = (fld1(x,y), mod1(x,y))
 
 # transpose
-transpose(x) = throw(ArgumentError("transpose not implemented for $(typeof(x)). Consider permutedims."))
 ctranspose(x) = conj(transpose(x))
 conj(x) = x