The phrase "this remains speculative" is correct and can be used in written English.
You can use this phrase when you want to express that something has not been proven or is not certain. For example, "Although there appears to be a correlation between increased sugar intake and obesity, this remains speculative."
However, given the diversity of fish in the Devonian, as well as the potentially paedomorphic nature of Protopterus, we consider it possible, or even likely, that fish existed that were capable of producing similar traces through this method of locomotion; though we realise that this remains speculative until more trackway data are collected from extant taxa.
This remains speculative only though as the majority of papers did not report on surgeons' experience.
Nevertheless, this remains speculative since no such region has been detected in human brain imaging studies [7].
All this remains speculative, however: the question of the question mark is not entirely settled.
At this moment in time, all of this remains speculative — since no one knows if Raul Castro will actually retire in 2018 as he has indicated he might, and no one can be sure that his retirement will be followed by the implementation of a democratic system or greater freedom of expression.
This remains speculative but worthy of future investigation.
Although Petersen emphasizes that any clinical implications of this work remains speculative at this time, the finding that multiple types of cells in breast cancers are capable of initiating invasive tumors, he says, could hold implications for future personalized medicine.
However this reflection remains speculative within the scope of this report.
This group however was more heterogeneous and this possibility remains speculative until a higher number and more defined groups of epilepsy syndromes have been studied.
Although this assumption remains speculative, several experiments performed in the present study support this hypothesis.
It's important to stress that this work remains speculative.
