We have 2 problems here: the first one is that the Lady Bird Johnson Wildflower Center is committed to the growth, protection and propagation of plants native not only to North America but the area in which they are being grown (in this case, Travis County.) The Meyer Lemon is native to China, as are most citrus fruits.
The second problem is that, even if non-native plants were in our area of expertise (which they are not) we would not recommend this tree for Travis County. See this Texas A&M University Extension Home Fruit Production article on Meyer Lemon, which notes:
"Lemons are among the most cold sensitive of all citrus. Because of the likelihood of damaging temperatures in most of Texas, lemon trees cannot be expected to survive for long outside the Valley unless special efforts are provided for cold protection."
This same article made this note about cold protection:
"Blankets, tarps or similar covers are also very effective and have the advantage of being quickly draped over the young tree. The corners should be stretched outward and tied down. More elaborate protection can be provided by erecting a frame structure of wood or PVC pipe over the plant to facilitate the use of plastic or large tarps during particularly severe cold weather. Supplemental heat can also be provided under the covers; incandescent heat lamps and Coleman lanterns are useful."