@Debra Richard *** This is not legal advice and I am not your lawyer. ***
I think the reluctance regarding series LLCs is based on the fact that they are new and in some ways an unknown quantity. I think they are really the best vehicle for real estate investors who own lots of properties.
That being said, I would not recommend converting an existing LLC into a series. That could be problematic. I would start one from scratch and then convey the properties one at a time into the new series LLC.
In terms of the potential pitfalls...
Some lawyers are concerned that courts will simply disregard the series structure and open the entire entity to exposure -- even though the statute specifically says that the assets and liabilities are segregated.
I really cannot imagine a Texas court "piercing the series" and simply disregarding the statute like that, but I suppose you never know.
There is some concern that states that do not permit series LLCs may not recognize them in those state courts--but again, how likely is that, that a foreign court would simply ignore a business organization?
And there is uncertainty about exactly how each series will be treated for federal income tax (and Texas franchise tax) purposes. Let me be the first to say I am not a tax lawyer, so there may be something definitive out there, but I do not think the IRS has affirmatively said how they intend to characterize series LLCs. I think there is an informal advisory note that says each series can check the box for itself, which seems to be the most logical choice.
I think the massive cost savings and organizational efficiency of the series LLC make it well worth the slight risk that any of these bad things will happen. Compare it to forming a separate LLC for each house, which has always been a nightmare.